There is a coherent distinction between the two cases (it's entirely fair not to think it's a distinction that you care about, but it's worth presenting the other side's argument right). The argument against Masterpiece Cakeshop was that gay people are a protected class in state anti-discrimination laws, and that the constitutional right to free speech (and free exercise of religion) does not include the ability to treat gay customers differently. "Being the president" is not a protected class.

(If you want to argue that a platform is treating people differently because of political affiliation, then yes, I'd agree that the argument about Masterpiece Cakeshop would apply - but it's far from obvious that any platform is in fact treating people differently because of political affiliation.)

Right, and they lost that argument because gays were not treated differently from other customers, since if a straight person asked for a gay wedding cake they would also be refused.

My point was not on the merits of the case, but rather that many people on one side demand that this be made illegal, and yet on the other demand that twitter shut trump up. They demand free speech for themselves while silencing critics.

It's not like Twitter is deleting his posts though? Just adding an annotation pointing out the lies (eg that California lets "anyone" vote when voters actually have to be registered.)

If Trump posted that America was being invaded by little green men from outer space would it be unreasonable to annotate that too?

I'm not sure that refusing a gay wedding cake to a straight person would avoid your action as being discriminatory toward a protected class, since that's the effect. Perhaps it would.

I also don't know that I would want Trump to be silenced, since he's often his own worst critic.

I don't think Twitter is stopping him from saying bad things, either; in fact, they're pretty explicitly letting him say things, and they just happen to have something to say about what he's said, too.