It's possible that there is a constant decrease in standards, such that every generation is worse than the one before it. But I doubt it. If such a steady decline had been happening since the 8th century BC civilization ought to have collapsed several times over. Tellingly, no one ever says "kids these days are much better behaved than we were as kids", even when it's empirically true. For example, kids these days in the UK drink less than their parents did at that age, but they don't get any credit for it.
What's actually happening is likely sampling bias, where the person making the pronouncement is looking at a few bad apples as well as nostalgia biasing their recollection of their childhood.