I've noticed as moderator that Americans in particular are touchy when you edit their posts, to the point of paranoia. This is why you should present it as FAQ comprised by you based on their submissions. This removes the need to defend your editing, as you can put up one explanatory post on how you're comprising the FAQ's. After that, there is no need explain the edits and people won't be so upset as you aren't presenting an edited version as their words, while still crediting them for the original work. That way, one post in advance should be enough defending and you can safely ignore the complaints or refer them to that one post if you feel obliged to reply.