It is morally wrong because it requires intervention to prevent two parties from engaging in what both deem is a mutually-beneficial contract.
This is patent nonsense, once you understand that a "mutually beneficial contract" is a fiction that already needs intervention to enforce. Contracts are pieces of paper with no value. They only have meaning and value because some government intervenes by deploying police with guns, and books with laws written in them, to prevent two parties from treating contracts as meaningless, which is what they naturally are in the absence of said enforcement.
In reality, of course, people have to have money to live. They have to have jobs, and a place to stay. Their lifespan is finite and they don't necessarily have the time to become experts at all the obscure details of Contract Law. The whole philosophical concept of people freely entering into mutually beneficial contracts is thus flawed in many practical situations.
Further, in order to be able to get a job in the modern technological world, people have to be able to learn to modern technological tools, which in many cases means access to software and other electronic media. Many such tools are commercial, and even the ones that aren't often require other commercial tools (such as an operation system), and as the use of commercial tools is often governed by "shrink-wrap" contracts, thus we run into yet another situation where the myth of two parties freely entering into a mutually beneficial agreement simply doesn't work in the real world.
If you listen to a typical Bar Review audio course on Contract Law, you'll probably hear the instructor plainly state that the vast majority of contracts are never read. Thus, the legal profession knows full well that these "mutually-beneficial contracts made with the full knowledge of the involved parties", are in reality nothing of the sort.
In the USA, understanding the law relating to contracts is extremely difficult. It's not simply a question of reading a textbook on Contract Law (which would be a challenging enough task in its own right, just from the length of the typical textbook). There's also a significant consideration most people don't think about (which might not even be mentioned in the textbook): in the USA the highest law in the land is the Bill of Rights. Clearly, as the Bill of Rights is the highest law in the land, it necessarily supersedes Contract Law when the two come in conflict.
To further complicate matters, James Madison deliberately gave the US an open-ended Bill of Rights, with unspecified rights "retained by the people" (9th Amendment) and "reserved to the people" (10th Amendment). He did this to deal with the objections made by the Anti-Federalists to the original Constitution, which the Bill of Rights would then supersede, namely that any Bill of Rights would be incomplete and would leave out really important rights that the people would sooner or later need to assert. This in turn has implications for Contract Law as it is ultimately up to the people to determine the rights retained by them, and those rights will supersede the established principles of Contract Law.
Consider the following: if any rights the people might want to assert as "retained by" or "reserved to" them could be taken away by the legal profession or by the government by any means, including some mechanism of Contract Law (or any court ruling or precedent), they would no longer be "retained by" the people: a contradiction.
For a concrete example, a right that might reasonably be asserted as being "retained by the people" is the right to long term oversight over business (we might also assert a parallel right to long term oversight over government, but that can be a discussion for another day). We don't, for example, want peanut butter companies letting rats get in their peanut butter that they sell: this used to happen, and hopefully as a result of public oversight over the conduct of businesses it doesn't happen any more.
A more modern example would involve the need for long term oversight over the environmental impact of a business. We don't want businesses dumping toxic waste and hence poisoning the environment, for example.
Note that the right to public oversight is not the same as government oversight. The whole point of having the Bill of Rights is that governments can be incompetent, or they can become corrupt. The presence or absence of government action does not preclude private action.
It is common to the legal profession put terms in work contracts that prohibit people from talking about their work (you might see the phrase "trade secrets") without any apparent consideration for whether or not, or to what extent, the presence of such terms infringes fundamental rights such as the right to long term oversight. This is a clear case of a conflict between Contract Law and the Bill of Rights (the existence of such terms does not say good things about the legal profession and it's relationship to the Bill of Rights).
Hence, to really understand contracts, you must also understand the Bill of Rights. However, it isn't sufficient to study what legal professionals think about the Bill of Rights, because the unspecified rights granted by the 9th and 10th Amendments are specifically retained by the people, not by the legal profession, and thus the views of the legal profession with respect to such matters are not binding. Putting this in other words: a government of the lawyer, by the lawyer, and for the lawyer is clearly not the same thing as a government of the people, by the people, and for the people.
Once we add Constitutional Law to the mix of knowledge required to understand contracts, that in turn opens up a whole can of worms, not just from the complexity of having to master yet another area of law (and reading another long textbook), but also because it is far from clear that the US legal profession's current view of Constitutional Law is actually consistent with the Bill of Rights or with some basic concepts regarding the ethical practice of law.
Putting this in hopefully clearer terms, the legal profession, as a class in society, is in a position of ethical conflict of interest with respect to the nature, scope, and form of the legal system. Contract law poses particular problems as far as legal ethics is concerned, because a) so much of the business the average legal professional engages in is contract related, creating an incentive to do the wrong thing in situations involving ethical conflict of interest on the part of the legal profession with respect to what can legitimately be put into a contract, and b) there's this built-in propaganda inherent in contract law that both parties "deem" the contract to "mutually beneficial", which in turn means there's a tendency to assume that if something is in a contract it must be "ok", which makes it really easy to conceal the legal issues (and the ethical conflicts of interest on the part of the legal profession) that often arise in contracts.
For example, in many "shrink-wrap" software contracts there are terms prohibiting reverse engineering. Does this not seem like a violation of the right to long term oversight of business (or even a violation of the right of the human mind to be curious)? If so, what should we conclude from the willingness of the US legal profession to put such terms in so many of these contracts?
Clearly, the legal profession is in a position of ethical conflict of interest with respect to determining whether particular terms present in a contract are legitimate or actually violate fundamental rights. The widespread presence of these "do not reverse engineer" terms suggests that the profession is not doing a very good job in handling the ethics issue in this particular case, which in turn raises questions regarding the ethical conduct of the profession as a whole (this will come as no particular surprise to those familiar with the issues involved in so many other areas of law, such as intellectual property law or tort law).
In short, to really understand the law regarding contracts, one must understand not only Contract Law, but also Constitutional Law, and Legal Ethics. How many people have the time to do all that, especially given that many of the conclusions they reach when they start to examine the whole mess are likely going to be different from the "party line" or the "official propaganda" presented by the legal profession as a class in society? It's far simpler for the average person to just assume that things will work out ok even if there was something bad hidden in the contract.