That is a pretty heavy burden you are placing on site creators... if you follow that requirement out logically, you are going to end up with some weird consequences.

So you say you shouldn't sell your site because the new owners might mess something up and harm users; does this mean you can't ever leave a company that you start? If you leave, the new people running it after you are gone might mess things up and harm users.

How is that any different than selling the company? In both instances, you are handing full control off to someone else. Just in one case, you are turning over control to someone you chose to hire instead of someone you chose to sell to. Either way, you are making a judgment call on their worthiness.

Are you really trying to say that if you start a company and want to leave, you have to shut it down?

This also seems to imply that when people sign up to a site, they are doing so because they trust a particular individual. Most people don't even know who the people behind a site are.

I think you are making out selling your company to be a bigger moral issue than it is.