That is right. I've blocked them too (used to work at a place that sent emails out). And the reason is the following: The person that enters such an email address does not want a long term stream of emails. Or anything. It basically makes the whole point of email "moot" (having an inbox).
Now, do I believe that businesses ask for email addresses illegally? Yes. You should not require to enter an address for e.g. a download. So we accepted Mailinator-type addresses but did not deliver (as it was too hard for us to detect new addresses). The usage of mailinator type addresses was a red flag on our customers as there was probably something wrong with the opt-in of that customer.
Second: Mailinator and other services are sometimes used as spamtraps. Now don't get me wrong, they have their uses. It was also in my interest to filter out the bad guys (so you needed some signals now and then even if you cannot trace it back). But not all of those services bounce inactive accounts. We have seen some weird ip blocks (where we could prove we, and our customer, did nothing wrong). Anti spam people are sometimes hugely incorrect in their assumptions / methods. The people surrounding such services were the weirdest I encountered.
Third: We would send out personal information. E.g. your name or other transaction related information. That information would end up "on someone else's harddisk". The PII and other elevated rights (e.g. "change email address to spam someone else") do not belong to an unknown third party.
But back to mozmail: We would not block. There are other services that are actually linked to a human recipient and has a gazillion forwarder addresses. We did not block those as the recipients would only be anonymous (which was fine from our perspective, you have that right and it is smart to know where you entered an email address).