Do you think it was a justifiable strategy to attack the buggers on their home world?

I think you need to think about this question in terms of what Ender believed he was doing. Playing a game and fighting in a real battle are two different things. It's the difference between reality and illusion..... and the reality meant death to an entire civilization. Ender felt he'd cheated.... even in reference to the game. The reality for him was an atrocity, which he himself had orchestrated. Thus, in terms of the game.... it would have been justifiable. In the real world, it was genocide..... never justifiable.