Let's face it. It wasn't just people being unwilling to accept a new show. Objectively speaking, TNG simply wasn't that great when it first came out.
That's true, but it did eventually find its feet. But at first, many were outright rejecting it, and I think I remember reading about some of the actors receiving hate mail (one of the ways toxicity was spread around). Eventually and much later, I think it was starting with the 3rd season, the show started to become more embraced and that toxicity started to fade away. Point is, people were vocal even then.