Like it or not, most Trek movies are action adventures, and that requres a villain to get the ball rolling. TMP and TVH were the only ones which weren't trying to be action adventures, and thus why they don't have specific villains.
Granted the problem with most Trek movie villains is that for the most part, they suck. Khan, and General Chang are easily the best, though John Harrison is looking promising. The rest are average at best. The Borg Queen was alright in First Contact, it's her Voyager appearances that tarnish the character. Sybok is in interesting character even if he isn't the best villain. Kruge, Soran and Shinzon at least were played by actors who made the characters somewhat entertaining. Ru'afo and Nero were just terrible.