Idées fixes

Definition: A fixed idea; an obsession, a usually delusional idea that dominates the whole mental life during a prolonged period (as in certain mental disorders).

Here are some of the milder variants, shared by whole swaths of the western world:

• Education is going downhill: children are still learning a lot (quite possibly more than I did when I was their age), and I don't mind so much if some of the things they are learning don't fit in the "classical" school curriculum.
• The youth nowadays has no respect! (see also the quote attributed - almost certainly erroneously - to Socrates). Some things are eternal, like noise and filth in city streets, and older generations being upset with younger ones. Every generation just reinvents this particular wheel; morals like discipline and obedience certainly go up and down, but had the trend been as systematic dowward as some people believe, western civilisation would have ended long ago. 
• Crime is on the rise: crime rates goes up and down, and are notoriously unreliable, because they depend on the willingness of people to report them, which varies according to their perception of whether reporting them will make any difference. 
• Each year is noticeably hotter than the last (because of global warming). In certain parts of the globe, average temperatures are indeed going up, but the differences are far too small and the variance far too great for an individual human to detect something like that. You need lots of measurements, taken by very precise instruments to reach that conclusion. (This is not the same as the phenomenon of the much more reliable method of calculating averages by asking many people to give their estimation - apparently much more reliable than one might think - because this concerns a change over time, which is not at all the same thing as estimating the temperature at any given point in time.)
• Old is good (or better): some old things are good (or at least good enough: the fact that they have survived so long is proof), and some are not. If things (ideas, beliefs, taboos, rules etc.) are lost in time, however, there is probably a good reason for that. Sometimes, solutions or rules that were perfectly good and useful in one type of society (nomadic, agricultural, or industrial) no longer fit the new situation, and often, this is because of the accumulation of information. The most common exception to this are the eternal truths at the core of most religions that are continuously "forgotten" because they are difficult to express and even more difficult to apply in daily life.