Whether or not there are other underlying issues stemming from such misbehavior is irrelevant to the fact that the misbehavior exists. It's like sticking your hand in a fire, then blaming your hand instead of your own stupidity for your third-degree burns.
Unfortunately such mechanism introduced a feedback loop in the presence of a bug in the kernel. I understand that it would be difficult for the kernel to guard from such loops, but my sincere impression is that they threw out the the baby with the bathwater.
The problem is that such collaboration didn't happen, and the systemd folks assumed that they were the center of the universe and decided "well fuck the kernel, we're going to use the 'debug' flag for ourselves, everything else be damned", thus causing breakage and flamewars. Had they taken the 10 seconds to write up an email on LKML or somesuch saying "hey, we think the 'debug' flag should apply to everything, not just the kernel; y'all game?", the vast majority of the fallout would have never existed.
Note that even Linus said that "parsing [the 'debug' and 'quiet' flag] and doing something sane with them is not a bug, it's a feature". So the issue revolved on what people believe is "sane", not about userspace using kernel bootparams (systemd still does and Linus is ok with it). The systemd folks argued that the kernel should not affected if something broke and started throwing too many messages at it during early boot (indeed, the kernel was fixed to rate limit in those cases). The kernel people instead said that it's not ok for userspace to flood the kernel, not even in broken setups (indeed, systemd was fixed to stop sending messages to dmesg as soon as journald is up).
I believe that sending emails here and there to ask "it's ok to do that?" would not work. LKML is already high traffic as is, such messages would just get ignored until things break.
"No, we very much expose /proc/cmdline for a reason. System services are supposed to parse it, because it gives a unified way for people to pass in various flags. [...] And yes, that does include "quiet" and "debug". Parsing them and doing something sane with them is not a bug, it's a feature."
http://lkml.iu.edu/hypermail/linux/kernel/1404.0/01488.html
> which is the actual bug that was filed (and in turn met with "it's not a bug it's a feature,
And that is the appropriate response to the bug that was filed, with the title "Do not parse "debug" command line parameter".
The bug report makes it immediately clear that this is not really about a technical problem that ought to be solved - no, the dirty user-space programmers should get their stinking paws off of our good kernel command line flags, how dare they!
Kay pointed out in his first comment that there is already a different parameter that turns on debug output only for the kernel; the reporter said he's too lazy to start using it.
And this is not about "entitlement": there is a clear administrative use-case for systemd using the debug parameter: if your system doesn't boot you want a simple and obvious way to turn on debug logging in all of the relevant plumbing code, whether it's in the kernel, in the initrd or during service startup. You shouldn't have to remember five different parameters because then you'll forget one and your outage lasts 10 minutes longer.
If the bug report had been something more like "I've enabled debug and my system failed to boot" without prescribing a particular fix and leaving that at the maintainer's discretion, it wouldn't have been resolved as NOTABUG but fixed quickly.
Of course, a wiser and more socially skilled maintainer than Kay Sievers would have immediately filed a follow-up bug report, or re-titled the bug report instead of lowering himself to the level of the reporter and playing resolve-reopen ping pong. (Fortunately the systemd project also also has some more patient maintainers like Tom and Zbigniew.)
Again, if you shove your hand into a fire, don't blame the hand (or, for that matter, the fire) for your own arrogance and stupidity. Common bloody sense.