The human aspect. What will happen (any blocksize really) if a powerful opponent fills the queue with spam transactions with high fee, like 0.01 BTC or even higher? A few million dollars could suffocate the functioning of bitcoin for months. My guess: As such situation is not advantageous for the miners despite the good fee money, they would find the spam transactions using heuristics, then fill blocks say half with spam transaction to take the good money, and half with normal transactions. The attack would be costly for the attacker, reduce the payment functionality to a degree, otherwise bitcoin would continue as always.
i was pondering this the other day. the best way to handle it? no limit. let the miners chew through high fees like that. is it even spam at that point? who cares?
those would be tremendous profit to miners and strengthen and drive the hashrate even higher securing Bitcoin even tighter. which ultimately is the last thing the spammer wants which would eventually cause them to conclude it wasn't worth it. and then stop.
If bitcoin ceases to have utility due to network disruption then it will also rapidly lose it's exchange value. That is not in the interest of miners.