The Debian init system general resolution returns

Two points to refute this:

1. KISS is not the only design principle that one needs to consider. Yes, it's important to keep things simple when possible, but it's also important to be efficient and provide users with the functionality they need.
2. You need to consider complexity at a system level, not just at an individual program level.

A good example of this is the Linux kernel. In theory, it could be made much simpler by adopting a microkernel architecture. In practice, we don't do that, partly because modular kernels have performance advantages and partly because it's really just pushing the complexity into userspace drivers rather than eliminating it from the system as a whole.

The same thing is generally true of the added complexity of systemd vs. sysvinit. Yes, the actual PID 1 is much simpler with sysvinit, but a lot of that is because it doesn't provide much in the way of functionality. Instead, that functionality winds up being provided by other parts of the system. By trying to keep PID 1 simple, you wind up with less functionality and more complexity in the whole system.