Well from the OT alone we know he was the kind of guy who tells Luke a lie in order to manipulate Luke into killing his own father because Ben couldn't do it himself.
Alright I'll say it - 'From a certain point of view'. The other way of looking at it is that Obi-wan and Yoda were trying to resurrect the Jedi as a whole and eliminating Vader and the Emperor were necessary towards that primary goal.