Did the prophet himself go kill people who criticized islam and/or his personality? I know of a sahabi who killed a woman poet who used to incite hatred against muslims and the prophet, but people threw garbage at the prophet, the tale of taif is very well known, and even there is a story about a bedouin who came to the prophet and started arguing that you are a bad muslim. A sahabi rose up and said that let me kill this person who dares disrespect the prophet, but Prophet Muhammad himself stopped the sahabi and said that let the bedouin argue with me.
This matter is very ambiguous and has no clear cut answers like what your mullahs in Pakistan make it out to be. This is even more telling considering the fact that the woman who was put on trial may not even have had said any blasphemous thing in the first place, so Salman Taseer shouldn’t have been murdered for expressing his opinion about that.