I can't speak for other systemd opponents, but I don't care much for it because it's so mind-bogglingly complex. I used to be of the opinion that it was particularly dangerous for pid 1 to accrete complexity, as more complexity created more spaces for bugs to hide, and a process-gunning bug in pid 1 can take down your whole system. With sysvinit, you could understand pid 1 with a few hours' study. With systemd, it's bloody near impossible no matter how much time you set aside. So accordingly, the attitude of Lennart & co. parallels Nancy Pelosi: "All distros should adopt systemd in order to find out what it does."

Systemd has a pretty compelling feature set, but I don't care if it fucking turns water into wine at this point; I've an allergic reaction to software complexity and abstruseness, and systemd gives me every reason to not trust it.