I don't think tail emission is bad per se, problem is bitcoin was designed to have only 21 million coins, and changing that fundamental property will mean it's as unsound as any other shitcoin.
Discussion
Yeah that's the clearest thing. But it's even true that if it had been created with tail emissions in mind and never changed the emission schedule, a future fork could have imposed a cap, which would make it potentially more competitive as a store of value, and therefore this fork could outcompete the original issuance fork. This is one of the reasons it's so brilliant that Bitcoin started with a fixed limit on the total there would ever be.