Because it can be economically expected that most transactions now are low priority, since fees are cheap. This means the actual transaction volume that likely would be taking place given only somewhat more expensive fees is much, much less. It's should be obvious enough that if transactions were completely free people would spam like crazy. That's not a judgment on the validity of those transactions; it's just economic reality. People start to economize dramatically when there is even a marginally-above-zero cost versus when there isn't.
This is in no way suggesting 1MB is sufficient, but it's not helpful to pretend that transaction volume when fees are negligible will remain the same if fees go to merely tiny. In no other market would we expect such a thing, and for all we know we could easily be talking about order-of-magnitude differences in volume from a fee increase that still presents no real pain for any major use case.
but cheap to who, you? i remember an Indian standing up at the San Jose conf during Q&A and complaining about high tx fees for ppl in his country. and they are, given their relative income levels.
we should be promoting Bitcoin to these 3rd world countries where a .0001 minimum fee is arguably expensive. that's why we have the economic fee choice of .00001 which oftentimes still results in rejection. to take it further, do you believe that Bitcoin should offer even these Indians the ability to buy a cup of coffee for cheap fees? i think so but probably you think different. i know tvbcof and iCE would flat out say no way. but then that goes back to my argument that for maximum decentralization and to become digital gold Bitcoin needs to service these ppl.
when you say ppl will spam like crazy, don't you trust that the miners can react to filter that spam, if they so choose? the problem with the 1MB choke approach is that yes, new users will be forced to economize on their tx's. OR just leave.
This isn't relevant to the question of whether having a fee market would help. I'm not saying 1MB is adequate, and I'm not saying that fees shouldn't be cheap enough for any particular group. I'm saying that no matter what blocksize cap we have, or even if we have no cap, we will still need a fee market for maximum scalability on chain. And we could easily be talking about order-of-magnitude differences in scalability contingent on the presence or absence of a proper fee market. As for miners blocking spam, sure, but as you say: who's to tell what is really spam?