That is a great principle and if someone attenuates harm concerns on a harm reduction forum, that doesn't mean we are all encouraged to just use obliviously... I guess there are those drugs I would want to steer anyone away from but yet others I would just more mildly redirect their course from for sure...
There are plenty of effects that can come from ketamine use that are worrisome, and even knowing those are part of the trip the effects from chronic abuse can still be quite troubling. For example the way it scrambled my sense of space and time was difficult for me for an annoyingly long time after abusing things like K or MXE. However I have demonstrated the same cat-like reflexes I had in the past since then, although other issues I attribute to things like ADD which developed late for me and remained hidden for various reasons.
I think the way the brain is affected from such dissociative use is largely reversible but perhaps for a small part much much less so. An example would be hyperpolarizable channels which appear to be responsible for ketamine's holing effects (and I similarly assume that other 2'-oxo arylcyclohexylamines share this affinity), my guess is that there happens something there which makes it so hard to truly hole again after a while while you can still get other effects.
It's possible there is something neurotoxical happening there if you accept your change = toxicity premise, but then it is really worth checking whether there is any indication of such neurological change actually having an impact on functioning whatsoever. This is a hard question but just as you are wildly going on reports, it would be equally valid to go on reports to be skeptical about neurological change meaning anything so serious.
Point is: I would warn people against ketamine even if I think neurotoxicity is a bit too big of a word in the context. The effects on functioning when you are using too much plus how addictive it is thus how likely that you will at some point be using too much if the conditions are right... those make me warn people.
I am still trying to peer through the ways people describe their history with K and other dissociatives but issues are not on the level of 'your brain is now damaged' like you might see with 4-MA or we are only just starting to piece together about NBOMe's. I don't have a good feeling about those or what they turn out to be and I am just happy I boycot the bastards after trying 2 of them.
But yeah, we will really have to be uncomfortably patient to wait what research shows us. Until then, yeah definitely warn people for plenty of fair reasons without necessarily mentioning neurotoxicity claims.
take care bud