Gattaca is fiction, with more attention given to having a good story than to realism.

Which was a success, it is a good story, and a movie I recommend.

What I think is that Gattaca, like most good dystopian fiction feels much more realistic than it really is, almost visionary. It is by design, it is a reflection of real world issues that readers/spectators are familiar with at the time of the writing, pushed to the extreme, and our natural negativity bias tend to make us forget the parts where the story was wrong in its terrible predictions.