Tough call. On one side I totally stand for freedom of speech as I believe it is fundamental that people be free to believe and say whatever they want. On the other hand, this guy is a total dick, no question there so he shouldn't be arrested but he should be totally ostracized in any and every possible way.
But arresting him is just as bad as what happens in Europe and how we let followers of that sick religion pour in by the millions.
I think the US and Europe draw the line with freedom of speech differently. In the US you're fine until speech becomes an physical act of violence, Europe when your speech promotes violence.
I agree the politician is a massive ****, but his tweet reads that he is happy that the guy is dead. Not an endearing view to say the least but doesn't seem he is promoting violence.