I know he sure was a kind person from flashbacks, something must have happened to him to change him like that, I personally don't hate him, and Natsu is just all out to fight him, i can understand him, Natsu's pure entertainment is in fighting strong opponents, be it enemy or friend, a good fight from the bottom of your heart is a good fight anyone can enjoy, Laxus just does something wrong right now, dunno why but I bet those two will solve the puzzle :]
their fight will be entertaining indeed ;]
Edit:Ep45
From the OP i knew Mirajane would fight seriously at some point in this arc, but she is damn awesome, I think she could be stronger than Erza.