You bring up two topics: the morality of gay marriage, and the completely separate issue of the financial and legal benefits the the USA government bestows on married couples.
You make a persuasive argument against the government giving special rights and benefits to married couples that are denied to other long term, stable relationships. I agree with you that the government has no business doling out special rights to some couples because they made a commitment called marriage while similar commitments are denied these benefits.
It is my opinion that government should not give any financial benefits simply because your are married. Further, I think the government should get out of the marriage business completely. Marriage, outside of religious ceremonies, should be replaced by civil contracts.A lot of people don't really understand that when they get married they are agreeing to a huge and convoluted legal contract. A range of simpler contracts should be available that spell out the rights and privileges of both partners: power of attorney, child custody and guardianship, shared assets, and how to dissolve the partnership would be some of the key things to include in these contracts..
The moral issue is should being gay be treated like being a red head, or being black, or being white, that is something that the law should prevent everyone from discriminating against.
In this case I disagree with you and say that being gay should be something that no one, and no law, can use as something to justify discrimination. Being gay is like having blue eyes, something you are born with. All government programs, civil rights, etc... should be available to gay people just as if they were straight.
And hospitals do NOT decide the rules about who can visit and who has the right to make medical decisions those are all laws - laws that currently discriminate against a lot of people. rules governing wills, child custody, etc... are also generally unfair to anyone other than straight couples.
Gay people are not forcing their morals on anyone. They are asking to be treated equally before the law. Asking for people to stop discriminating against yourself is not forcing your morals on anyone; it is asking for the law to be fair.
Finally, gay people are not "greedily" grabbing benefits they are just asking for the same benefits others already have, and you so eloquently argued that everyone should have. Are you saying that all committed, long term relationships should get benefits, except gay ones? That would hardly be moral.