Of course it's difficult to name the exact test that draws a bright line between legal and illegal speech, because speech exists along a continuous spectrum. B

Of course it's difficult to name the exact test that draws a bright line between legal and illegal speech, because speech exists along a continuous spectrum. But the law has literally hundreds of years of experience with such problems. The line between marketing and fraud, or porn and art is just as hard to define. So, for example, bringing Swastikas to a protest in Germany would get you thrown in jail, and so would guns, or slogans such as "gas the jews". It's been like that for 70 years, and you're still free to say really nasty things about Merkel without any fear of prosecution.