I guess many that are against it, would rather have a pure UNIX V installation, eventually running twm.
I don't think Linux would have gotten this far if its core wouldn't be influenced by the design principles of Unix and the kernel project wouldn't be run by a person who takes care regarding incompatible changes. Look at ReactOS or Wine. I'm worried that systemd might prove to be a major headache in the future.
In my experience, systemd fails on both points. For example, and understanding of user permissions under systemd is probably beyond 99% of developers' expertise.