A lot of people used to play with 68 round magazines without any issue. If you're trying to shoot through crap that easily deflects BB's, move. Since when did airsoft become a sport where you sit on your ass in one place?
I also don't really like the "1 BB isn't equal to one bullet" argument. While true, if people are having that much issue getting rounds near their target that they need to use a ton more ammo to compensate, they're engaging from too far away or in a bad position. I say learn how to use your AEG and move to a better spot, instead of just compensating by filling the air with BB's.
My argument is more how AEG assault rifles and SMGs seem to be used more and more often as support weapons, and people actually have the ammunition to do it. The favoured tactic now seems to be "have 3 people hose the guy until you get a kill through sheer volume of fire" rather than actually using proper tactics to advance, flank, and kill that way. Heck, trying to get people to advance now is like trying to pull blood from a rock. When you don't carry 1,000 rounds on you, you're forced to move and advance, because you don't have the ammo to sit there and get kills through volume of fire. When a skirmish goes on for 10-15 minutes, with everyone constantly firing, nobody moving, and nobody getting hit.. I think there's something wrong.
"Someone in a Prius tried to race me at a stop sign the other day. I couldn't believe it. I had him for the first 100 feet or so but I can only walk so fast."