I don't see them being hated. Seems more like an issue many players have with Grass being statistically one of the worst types in terms of type match-ups, making the other two seem much better choices.
Sure, we know that what matters at the end is the team, not each Pokémon individually, and there would be times in which a Grass type might be just what a team needs, but since the starter is the first Pokémon, and many players seem to build their teams around them, picking Grass feels like starting off on the wrong foot, as there will be allways more weaknesses and things to worry about compared to Fire or Water, which offer a more solid team building foundation.
Personally, Grass is my most used starter type, and one of my most used types overall. I had every Grass starter in at least one team so far, except for Chespin and Sprigatito, and five of them have been my first playthrough choice. My favorites are the Turtwig and Rowlet lines.