How many times do people, in their lifetimes, buy something that doesn't exist at the time they purchase it, with the expectation that it will come at some point in the future? I can think of a few - like building a house. You pay contractors for work, and at some point you should have a house to show for it. You pay for tickets to a show with the understanding that the show will happen when they say it will. I'm sure you can think of other examples as well.
The difference is that most of these examples involve a contract, which gives you recourse if the other side of the contract fails to deliver. You can take the contractor to court (jury, small claims, or arbitration) if they don't deliver your completed house by the time set out in the contract. Many times there are clauses in the contract to redress these issues - such as SLAs (service level agreements), giving you financial recompense should the service not be performed at the specified time in the contract.
While I totally understand the frustration some people have with FSD, I'm not sure what options are available to them. As has been stated, the goal of delivering FSD has been pushed back repeatedly over the years, since 2016. But there has never been contractual obligations from Tesla on these dates (it's always been stated as "coming soon"). And there is no legal action you can take for broken promises (Elon's tweets regarding when features will/should be available), except in cases of promissory estoppel, which forms a contract between both parties.
We should have seen thousands of lawsuits, or at lease massive class-action suits against Tesla since 2016. Court orders handed out forcing Tesla to change their FSD sales practices due to violating consumer protection laws or commerce regulations. But we haven't seen anything like this in the US.
On the contrary, Tesla, since 2016, has become one of the highest valued car companies in the world. They sell every car they make, even today, with many people waiting months to get their car delivered. And the most damning statistic of all is repeat buyers. Tesla has one of the highest brand loyalties in the industry with over 70% of buyers purchasing another Tesla. If people were so pissed with Tesla over FSD and broken promises since 2016, why are they going back? Even poor build-quality, which was widely reported in media, didn't seem to stop people from buying and re-buying a Tesla.
There are definitely people who feel duped and cheated for their FSD purchase. It doesn't matter what anyone says, such as "buyer beware", it's just not going to ease the sense of outrage they have. The only thing they can do is hopefully change the company through the free-market - vote with their dollars.