Re: Not an expert, but...
"so why fight a purity war"
It's not a purity war. Most of us are init-agnostic.
However, the systemd-cancer actively and intentionally breaks software. One should be able to switch inits on any given system without breaking software compiled for that system.
In essence, the systemd-cancer is an answer to a problem that nobody had. Throw in the fact that it's sticking its tentacles[0] into places where nobody in their right mind would expect an init as a dependency (disk partitioning software? WTF??), can you understand why us "old guard" might question the sanity of people singing it's praises?
[0] My spall chucker insists that the word should be "testicles". Tempting ...