Can you rephrase your example in a way that doesn't include a protected class/characteristic?

Can I try?

You decide to print pamphlets for your protest after a colleague is fired when your boss/admin/whoever found out she had an abortion.

You ask the printing press to print pamphlets for your legal, peaceful and just protest. They say no, they'd rather not be involved in that sort of thing.

Do you still support this idea that businesses should make careful judgements about each client versus a general policy of neutrality?

In my country she wouldn't have been fired in the first place. At-will employment is just a way to bully people into toeing the line.

Putting that aside, yes: Political speech shouldn't be compelled, any more than it should be constrained.

Now if you want to put some kind of further "common carrier"-style legal burden on printers (or kickstarter), then I think it's possible to make a case for it, but I'm not personally in favour. (On the other hand, in the UK we do exactly that with bank accounts - it's nearly impossible for a bank to turn away a new customer - so I guess there's a case for it in some circumstances). It's ultimately a question of regulation I guess.

Just turn the clock back to before the protected class was declared and their example is valid. If you don't like that, imagine a hypothetical future protected class that is currently not yet protected for surely there will be one.