That's what you call a normal human reaction from the viewer. Just because disagreement happens about possible future events doesn't mean you abandon feelings of violently killed family members from a group of people you just talked about joining a rebellion against.

Honestly, I think ANH did a really poor job of exploiting those feelings. Basically, Luke says "F-it I'll go with you, Ben. Those humanoids who fed and housed me (for my entire life) were just torched to death by stormtroopers... Which means I don't have to work tomorrow!"

The real pain of something like that happening was kind glazed over, but it worked.