There is no need for city defense anyways, since high defense won't stop a moderately boosted attack. Collect on time, no plunder.I'd only be guessing but I think Emberguard hit the nail on the head. If a player can aid all of his hood, friends and guild with a single click (or maybe 3 clicks?) I think that most would do so when a large percentage don't currently. I would think that this would eliminate plundering (140 friends, up to 80 guildmates and 70-ish hoodies = lots of polivated buildings = no plundering = no need for city defense)
In most cases non-motivated buildings don't get their better collections anyways so were never worth plundering. With just a few exceptions the only buildings that have ever been worth plundering are those that can't be motivated in the first place. An aid all button wouldn't affect plundering to any great extent.