Both optimists and pessimists are wrong. If the complaint about the young is defensible, it does not follow that the world is going downhill, contrary to what everybody believes. The distinction between age and cohort effects comes in quite handy here.
Let's start with complaints about the young being ill-educated, meaning that they don't know things "one ought to know". Obviously, what "one ought to know" is pretty subjective. Once generations disagree about that, the stage is set for generation A's complaint about generation B's lack of what generation A deems to be essential knowledge. If they cared enough, the young might as well chastice the old for their ignorance. For example, my father could teach me quite a bit about European history, but I'm pretty sure he has no idea who or what Kurt Cobain or Darth Vader were or are. I think these are things one ought to know. So, that's a cohort effect.
Complaints about the behaviour of the young come in two flavours. One refers to behavioural standards it is easy to disagree about. Some people think, "no brown after six", others don't. But you'd have a hard time arguing that there's something inherently wrong about wearing brown shoes to a formal evening event. So this is basically like the problem above - cohorts disagree, and no one is objectively right.
The point is that in both cases complaining about the young and the observation that such complaints have always existed lead to no contradiction. You might well think that it is exactly your generation that got everything right. In which case you should wake up every morning shouting, "I'm so grateful for being part of my generation!"
But not everything is a cohort effect. The other complaint about the young - the one heard most often - is that they're loud, boisterous, aggressive and generally unruly. Let me submit that this observation is, and always has been, totally correct. An extreme manifestation of this is that in almost all places at almost all times that we have data for, we see a massive overrepresentation of the young, and especially young men, among the perpetrators of homicide (see pp. 109-15 of this academic paper). The error that both pessimists and optimists make is to mistake age effects for cohort effects. Pessimists think that the behaviour of the young is indicative of the behaviour they will show throughout life, and conclude that we're doomed. Optimists accept this general logic and argue that it ought to follow that we're already doomed, as people have always complained about the young. They conclude that the observations about the young must be wrong.
But both are mistaken. Applying their logic, pessimists should predict massive lifelong hygene issues in the current cohort of babies. They all shit in their pants! They'll need diapers all of their lives! Optimists should counter that the observation about the low hygene standards of babies compared to other humans may be found throughout history, which should lead us to conclude that by now we're in hygene hell. As we're not, the observation that current babies all shit in their pants must be inaccurate.
But it's not. Babies shit in their pants, young men are aggressive. That's the human condition in a nutshell for you.