No, I mean the blockchain would literally collapse. Not in a figurative sense. The blockchain could not function if your proposal was implemented. The flagging of spam accounts by spaminators, mackbot, etc. serves a vital purpose. If spammers could simply choose to not be flagged, the entire thing would literally collapse. The levels of spam posting would increase past the point that the witness servers could bear the state cost and even the top witnesses would be operating at a deficit. The only other alternative if spammers could choose to not be flagged, would be that the RC costs of making actions to the blockchain would have to be raised up so high that no users could transact at all except the absolute biggest whales.
EDIT - let me put this another way. I don't want to dismiss your 15 years of experience of thinking about these issues in the "real world", but in a very real sense, that experience isn't particularly relevant here on the Steem blockchain. You are absolutely correct that in a non-blockchain setting, if you could simply subscribe to a spam list and not see the spam posts, there would be no harm to you. But on the blockchain, whether or not you can see the spam, there is in fact a cost to you and every user for spam posting. The current RC costs per action are based on the current levels of activity on the blockchain, so you (and every user) are paying a price for the current levels of spam posting. We can say with absolute certainty that if spammers could choose to not be flagged, levels of spam posting would explode. This means, again with absolute certainty, that the cost to you and every other user for that spam posting would increase. Do you understand if I put it that way? The victims of your proposal would be those with the least steem power, as the cost to transact on the blockchain would price them out of using Steem at all. And if the levels of spam increase to the point that I am certain they would if spammers could choose not to be flagged, I think only very large accounts could actually transact. This would prevent spam, but it would also prevent... all other legitimate uses.
EDIT part two: I actually think the only real solution for a blockchain based social media site is to eliminate monetary reward. As long as there is monetary reward, there will be abusers manipulating system for reward, and flags will be a vital necessity to keep the system working. I would love to participate in a Steem clone that had no tokens, no payouts, but was just a truly decentralized social media network with the censorship resistant benefits of blockchain. I know myself and many others would use it even for no rewards. Heck, literally billions of people use Facebook for no reward.