Speech is never without a cost, but what the First Amendment does is it comes as close as law can get[1] to completely cutting any kind of prosecutorial slippery slope off at the kneecaps.
Don’t forget the context within which the First Amendment and similar laws exist: to blockade government authority to prosecute you because something you said was heretical, of a different political position than the government’s, or because you hurt someone’s feelings. You can still hurt someone’s feelings, it still has consequences, but our (American) legal regime is such that this is not an offense worthy of conviction.
[1] As close as law can get. I have learned over the years that invariably the very first response I receive, if any, will be one looking to poke holes in a perfectly sweeping statement I didn’t make because any and all nuance is overlooked and hedges ignored. Prosecutors can still abuse their authority in other ways, anyone in Government can, that’s why we put limitations on the SOBs in the first place. Any written (or unwritten for that matter) law you can conceive of, no matter how well written or conceived, has to face off against human ingenuity.