And some opinions cannot be tolerated in a democratic society. An obvious example is anti-liberal/anti-democratic opinions as they threaten the system itself. You cannot have a free democratic society if a majority removes the freedoms of a minority.
These are not contradictory - they are both essential freedoms.
Very weird interpretation of "voluntarily choose to not continue supporting them financially"
Presumably you want everyone to be forcibly compelled to finance the political parties they disagree with? And you would define this as a democratic society?
What % do you think a reasonable voter should accept a person donating to a political campaign before it causes concern about the donor's influence vs the median household's voice?
Off the top of my head, I'd guess 500k USD is about 1000% / 10x median annual household disposable income in SE, which I think would give the median voter pause.
For what it's worth (my own view): I think about 10% (~5k USD) is obviously acceptable, and I expect most anyone would agree that donations at that level are fine. I think your proposed 1000% is obviously unacceptable, and I expect most people would agree with me on that as well.
I'm not sure exactly where the level is that opinion would flip, but I feel pretty confident about those boundaries.
[0] I suppose unless they have a very influential position and it's about a matter that contradicts main company goals
Is that somehow undemocratic?
Is anyone censoring the guy?
Nobody is calling for violence though?
In a free democratic society nobody is forced to do business with anybody they don't agree with, and free speech means they can talk about their decision without fearing repercussion.
https://knowyourmeme.com/sensitive/memes/richard-spencer-pun...
And if I disagree strongly enough then I am free to take my business elsewhere. Especially if the money I hand over might go to support speech and parties I fundamentally disagree with.
Freedom swings both ways, and freedom of speech doesn't mean freedom from people thinking you're an asshole and not wanting anything to do with you. That's their freedom.