Imagine that time travel is invented. Not now, it's invented in the year 2875. The future people came back in time to this period to give us knowledge of how to build time machines so we could explore time freely. They also gave it to every other time period. Ancient egypt, the roman empire, alpha centauri, the 1960s, the reign of king arthur, victorian england, they're now all places you can just go. Time travel is as cheap as a plane ticket.

If that happened, then the sorts of people who currently claim that the 1960s were the greatest period in human history would probably change their minds. Not because of any sensible reason, but because the 1960s are now a Foreign Place. They'd start being xenophobic and complaining about all the immigrants from the 1960s stealing jobs and living on welfare. They'd be racist against the past. They'd keep on listening to Beatles and Pink Floyd like it's the only good music ever written, but they'd scoff at all the hippies on the other side of the time portal.

And not just the 1900s, either! The romaboos would probably call roman empire immigrants racist slurs. Those neo nazis who wear norse runes would go back in time to do hate crimes to actual vikings. Weebs would say the Edo period just "doesn't get it". Science fiction fans would accuse the future of being woke SJW trash.