He didn't care how they survived on the island alone he just wanted to go home to see his auntie that he has been missing for the last couple days. Piggy wanted off the island because he didn’t like Jack because Jack killed Simon, and Piggy was friends with Simon and was mad that he passed away. Roger is one of the british boys that are stuck on the island alone, and he is basically the slave of Jack and also on the bad guy side trying to take over the island and they are willing to kill anyone in their way. Piggy is basically the slave of Ralph and also on the good guy side and all they want to do is try to survive and live on the island until rescue comes and saves them.
All in all Piggy and Roger were doing what they think is right. It may not have been the right thing to do in real life, but to them it was the right thing because they were stuck with one person for a while and they looked up to that one person and what that one person did Piggy and Roger followed along and did also by themselves. They really didn't mean any harm until Simon died and that's when both groups of boys should have realized that this is serious that someone, one of their friends just died but they didn't stop from there they kept pushing the matter of civilization or savagery and then Piggy dies and that's where it should've ended again.. But no they kept going with it and Jack's group even tried to kill Ralph to but luckily