(As far as I know) only those scholars who support death penalty for blasphemy.
For example, they give the example of Ka'ab (or whatever his name was) who used to insult and lie about the Prophet. He was given the death penalty by Prophet Muhammad at the conquest of Makkah. These particular "scholars" use this to prove the punishment of death for blasphemers.
A more detailed look at the events shows us that Ka'ab (again not sure about the exact name) was first a Muslim, then he got angry with his slave, murdered him, apparently fearing retribution from the Muslims, he joined the Makkans and also instigated them to fight the Muslims.
Therefore, depending on the conclusion/agenda a group of "scholars" want to push forward, the same event is looked upon from different angles.
I personally have not come across a single reliable narration that unequivocally shows that a person was given the death penalty specifically for only insulting the prophet. While on the other hand, there are many occasions that we know of, when the blasphemers were not prescribed the death penalty. The forgiveness of the whole city of Makkah - which included many who, forget about insulting, actually fought the Prophet - is an interesting event in this regard. The argument that these "scholars" are apparently giving is that trying to actually murder the Prophet is something for which forgiveness can be asked for (and given) but not insulting him. Additionally, it isn't as if the Kuffar tried to kill the Prophet but insulting him was where they drew the line. It is very much likely, they insulted the Prophet too. So, according to the death penalty supporters, fighting or fighting+insulting the Prophet is forgivable but when the Prophet is just insulted, it is unforgivable.
