What about PoW (https://en.wikipedia.org/wiki/Proof-of-work_system https://en.wikipedia.org/wiki/Proof-of-work_system) ? It require minimum user interaction, a

What about PoW (https://en.wikipedia.org/wiki/Proof-of-work_system https://en.wikipedia.org/wiki/Proof-of-work_system) ? It require minimum user interaction, and you will eliminate most of spammers bot, since it will lose its cost-effectiveness. You can implement something like coin-hive proof-of-work, without having to mine monero anyway