Incitement is illegal, yes, because it indirectly infringes on others safety and freedom. By encouraging violence against a group of people, that group is put in danger.

Luckily, there is a justice system that can apply nuance to each case, so that people can be convicted of inciting violence even though the do not explicitly threaten anyone. A "thinly veiled threat" or implications can be enough.

My opinion is that we have robust laws in place to prevent threats, incitement of violence, etc. adding blasphemy laws restricts freedom of expression without adding any protection of value.