You can either discuss the concept of free speech, or the first amendment. You just conflate the two to legitimize acts that go against people freedom of speech/expression.
The first amendment only limits the government from incurring penalties to the expression of its citizens. It does not, however, deal with other citizens who penalize others for speaking their mind.
Freedom of speech (the idea), is freedom from consequences. The only limitation is where your free speech might interfere with the same freedom given to others. In short, you cannot use it to silence others, which is exactly what you propose.
Milo mocks progressives by calling his tour, “dangerous fagot.” It’s a criticism of what people consider dangerous. I have listened to a few of his talks he does not discourage speech, on the contrary — but I doubt you actually listened to anything he actually said.
As for the university, after the invite to speak on campus, the university has no right to cancel the event, other than when there is a danger of bodily harm. Otherwise, they should be legally bound by the fact that they are a government-funded institution.
The florist should be able to serve whomever she pleases, but when you have a law defining some group as protected than other laws get abused. This case the spirit of the law was crushed for the benefit of the word of the law.
The real question her is different. Will you support everything you’ve written if it becomes popular that Atheism is obscene, that homosexuality is a perversion or any other idea that is important for you to protect? Will you still support a ban on anyone who talks in support of those topics? Will you try and claim that they are within their right to freedom of speech?
People are creating a weapon. The weapon could be wielded by anyone and for any purpose. Only, that the people making the weapon believe that they are the only ones who can wield it. History tells a different story.