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.
It will cost 40 BTC per block, 240 BTC per hour, 5 760 BTC/day, 40 320/week, 161 280/month and 1 935 360/year. ... I'll hold or just pay 0.0101 per transaction :-)
but can't you see that w/o a limit Bitcoin actually could inflict huge economic losses on an attacker that keeps trying or goes too far. there's a dark, unknown ceiling there for him that could inflict serious losses. i for one would love to see that happen as it would strengthen miners greatly as well as Bitcoin generally. this is what we've always wanted for miners; fee income security to replace block rewards. no amount of block heuristics, rules, limits, or sizes can predict the appropriate amount of "regulation" by core dev. they need to open up the limit and let free mkt forces run. b/c Bitcoin is open and honest, it will crush anyone wanting to damage it thru nefarious means.
You are right, but there will always be a limit to capacity somewhere. Even when the physical limit is approched, bitcoin payments will continue to function, due to the above.