I actually think the practice of going in with Gorillas is hugely beneficial to them, and in stark contrast to Elephants and Tigers has never resulted in any fatalaties.
I think being able to interact with Gorillas is useful in terms of being able to treat them during illness etc, but not every Gorilla enjoys the close company of humans. For example; the female 'Kaja' (who is now at Chessington) consistently rejected human attempts to interact with her at Howletts and would 'cough threat' when anyone tried to engage her in play.