Facebook doesn't give a rat's ass about protecting users from Trump; they want to protect themselves (and their customers, without whom the users have no reason to keep telling Facebook which of the customers' ads they want to see). They want to not get sued or indicted for aiding and abetting crimes, torts, etc. They want to cultivate/protect their image. They want to maximize sales revenue.
Don't they have the right to protect their own interests? If I want you to put something on your website, you don't think it's reasonable that you should have a say in whether or not you have to do it?
Should Disneyland be compelled to host a porn convention? It's not about whether or not you think they should do it, or whether porn is good or bad; it's about who gets to decide what Disney's assets get used for, how much (if at all) Disneyland should be forced to work directly against the image they want to create for themselves, etc. Just as Disney doesn't want to be associated with porn, ad companies don't want to be associated with fraud. We sometimes disagree with them ("porn isn't bad!" or "Trump supporters deserve to be parted from their money!") but it's not our decision to make when it comes to someone else's website.
It is your decision on your website, though, and if the government or a private company ever tries to censor you, you can count on my support. But I have the usual warning to leftists: don't confuse your right to be left unmolested, with an entitlement to the use of other peoples' resources. Nobody has to help you .. yet. Maybe America is eventually due for a Communist revolution and we'll start allocating resources the way you hope, but it's insane to already think of it as a done deal, and until you make it happen, the rest of us are proceeding with America-as-usual, and I'll even admit plenty of us oppose the proposed change.
Imagine Thomas Paine being compelled to give space to a British rebuttal in his Common Sense pamphlet. That hypothetical story alone, might inspire me to pick up my musket as much as the rest of the contents of the pamphlet! (So, naturally, I'm sure the story will be circulating on Facebook in 3 .. 2 .. 1 ..)