This is what many people view un-unix like, a big dependency, that can't be replaced in the chain. The systemd developers also develop udev (which actually builds out of the same source tree as systemd), and there have been a few arguments about whether certain responsibilities are that of the kernel, or udev/userspace http://lwn.net/Articles/518942/, http://lwn.net/Articles/593676/. Systemd also touts its cgroup usage, though they view that they should be the only user of cgroups, since they are in a spot to "manage things properly" (which is partially true). (Some services have also started relying on systemd's cgroups to clean up orphan processes, which is bad for other init systems that don't do this).
So no one really hates how systemd works, just how its managed, and what it aims to do. If it were a simple init system and service manager, there would probably have been no arguments.
