When it comes to owning a share, it eventually needs to make the investor money through dividends or price appreciation. The argument for high PE ratio is price appreciation (growth), but exponential growth is very hard to sustain, so PE ratio has to come down to a certain level in the long term. Also, there is always a risk of a company declining or even folding.
At least you have to actually look in the eyes the guy you are screwing over.
You can't buy stuff because you think other people will also buy, that would mean that you are buying/selling opinions not companies.
If you can predict the next hype cycle or when exactly this one will end, you will make a zillion dollars.
If you are talking about entire markets rather than individual companies then p/e matters because the only examples we have of markets with extreme p/e ratios all ended in disaster.
You should still buy stocks for the long term regardless of PE ratios because you're right, it's not possible to predict what they'll do. Unfortunately when you buy at a high pe you can't anticipate as much return in the future, all else equal.