Your argument assumes that systemd is simply meant to be a in-place compatible drop-in for what it replaces, which I don't think is something anyone would/should expect. If systemd was meant to behave the exact same way as systems it is replacing then there wouldn't be much point of it. For those cases it sometimes will break things, and will sometimes have settings to follow previous behavior.
There's plenty of room within the POSIX specs to address service management without requiring kernel integration, breaking userland tools, etc. When your init replacement manages to interfere with the kernel you've done something very, very wrong.
Not sure if I missed something here but how has it interfered with the kernel? AFAIK it has broken some userland tools (which is bad in itself in most cases), but actually breaking kernelspace is not something I've heard of.
Yet just two days ago, we see Linus Torvalds (the creator of Linux and maintainer of the Linux kernel), launching into a tirade against – yes, you guessed it – systemd developers because of their atrocious response to a bug in systemd that is crashing the kernel and preventing it from being debugged. Linus is so upset with systemd developer Kay Sievers (gee, where I have heard that name before – oh, that’s right, he’s the moron who refused to fix udev problems) that Linus is threatening to refuse any further contributions from this Red Hat developer, not just because of this bug, but because of a pattern of this behavior – a problem for Kay because Red Hat is also foaming at the mouth to have their kernel-based, no doubt bug- and security-flaw-ridden D-Bus implementation included in our kernels. Other developers were so peeved that they suggested simply triggering a kernel panic and halting the system when systemd is so much as detected in use.
The key phrase there is:
a bug in systemd that is crashing the kernel and preventing it from being debugged
Honestly though when you get Linus flaming your behavior you're doing something really wrong.
Likewise, of course, or you'd know that the tirades were more often than not in response to things that were indeed "really wrong" (at least by his standards).
