You seem to be under the illusion that if Facebook banned nothing (or at least nothing that goes beyond what is illegal), they would not make a moral decision.
But that is wrong. Deciding to allow absolutely everything is a decision (e.g. by placing higher moral value on freedom of expression than on other things) just as much as deciding to disallow some other content is a decision.
In the end, there is no escaping morality. As a human being, it is your responsibility to make decisions according to your own moral standards (and the limits of the law) and if you're someone with power, these decisions will affect more people and will be scrutinised more.
> Who decides what is moral and what is not?
Everyone decides for themselves. And then we come together as a society and we figure out what to do about the messy differences between our positions and find some sort of compromise - that's really the only way it goes.
LGBT is just an example, because in many cultures it is immoral. As is the nipple.
I just don't think it's a good idea for a private company, to be able to decide arbitrarily what is moral and what is not. Especially facebook.... there are many bakeries, but not many social networks with billions of users.