I also love the systemd init system and unit system. What most people complain about isn't that. It's all the rest. Systemd is a huge, huge thing that tries to do everything.

Here, people are complaining that systemd replaces the name resolution system. People also complains it handles tmpfiles, the random devices, the journal, etc... People complains that it replaced perfectly working, battle-tested components with new, unaudited code.

I don't personally care one way or another, btw. I'm a happy systemd user. But I understand the concern.