For me, it is pushing Linux in the opposite direction of the main reason why I like Linux.

I was attracted to Linux because unlike Windows or macOS, I actually have choice with Linux. I can choose my filesystem, my libc, my init system, my bootloader, my system encryption, my window manager, etc.

Sure, it's not perfect: many programs assume that you have glibc, or dbus, or X11, or wayland, etc. Actually many programs assume that you run Ubuntu. And it is frustrating when you would want to use a program and can't because of such an assumption. But again on Linux, there is (or used to be?) a big open source culture. This program is assuming glibc? I can patch it to work with musl. Etc.

Systemd, to me, sounds like it says: "why would I care about interoperability? I am the best, you should use me. And if you want something else, you should make that something else interoperable with me, because I make the rules". It's not like systemd is trying to standardise stuff to allow alternative components to exist, right? It doesn't actively try to prevent alternatives, but that's pretty much it.

And normally I wouldn't care (again, Linux is about freedom of choice for me). But systemd being as successful as it is dramatically reduces my freedom. And systemd it seemingly trying to take over more and more components. And the more adoption it gets, the more power it has. You didn't want systemd to replace that part of your system? Too bad, it will. What are you gonna do anyway, systemd is too big to care about you at this point.