Since you mention the early internet, some of the earliest websites I remember would have a 'number of visitors' counter usually in the footer. Which in and of itself is an early form of that validation you speak of. When you found a site with lots of visitors, it validated the site, made it seem more legitimate. And lots of early web site owners would react the same way to a new visitor to their page as a user reacts to a like today.

Validation culture has always been in some ways a part of the internet. Even before the things I spoke of. But I agree though, today it's taken over too much of culture in general. Whereas back in the day, someone may be happy or excited, chances were it didn't affect their life much. Now people's entire lives and fortunes exist because of those validating likes.