We have to be aware that every party in.the chain should get their fair share. So transactions can't be free, this is mot sustainable. But at the moment I think that fees are reasonable and with time they will probably get lower. With new technologies and new energy sources miners will find the way to lower the costs and that will probably affect the fees.
Maybe at some point in the future, after several halvings of the block reward, the reward will be so small that transaction fees will be necessary, but not today. 12.5 BTC, the current block reward, is still much higher than all the transaction fees combined. If nobody was paying more than $0.01 per transaction, or even any fee at all, the blocks would still be mined because of the block reward.