You make an important point: constitutionally-protected speech is the strongest link in their defense.
These people almost always have social media accounts, personal website hosting, and other business arrangements. None of this business is constitutionally protected and all of these business partners can be identified and many can be persuaded to cut ties. For years people have been using vague untargeted appeals to decency and it has gotten no results at all. We need to target their business partners with boycots and consumer education in the same way that wish.com became a synonym for low quality.
I am dubious about boycotting, it’s akin to an appeal to decency, and those that are the worst for the environment are so entwined with the goods we consume, that it would take hyper awareness to realize if you were actually following the boycott if that was one’s goal. I think much more extreme measures would be necessary to compel change.