We know Sam is pissed that Daenerys killed his father and brother. But the conversation he has when telling Jon is stupid beyond belief! Would you have killed my brother and father? Why would Jon know she executed them? I'm sure she didn't go around telling everyone who she executed and then she was supposed to know it was Jon's friends family? And you were always king? How stupid!
shareI think he was trying to make a point of why he thinks that Jon would make a better King (obviously also reasoning while being emotional) - he asked if it was him, if he would have killed them just because they didn’t bent the knee.
I also don’t think that he really thought his arguments through- he was emotional and just found out that his father (probably didn’t care THAT much) and his brother, whom he DID love got killed. So sounds pretty reasonable to me considering the circumstances.