You can argue that an illegal thing should be legal without inciting people to do it while it's illegal. Under your reasoning, any act of inciting violence could be dismissed as "discussion".

There's probably not a clear line in every instance. Whether you think "praise and support" crosses the line, it would be pretty hard to claim it made things better, and pretty easy to see how those words, from the most powerful person in the country, might make a person more likely to continue doing whatever it is they're doing.