You make a good point, Dekelso.
Certainly, there have been those in the Federation and elsewhere that have proven themselves implacable enemies. For instance, there was the Borg, as well as the conspirators in Star Trek VI, who wanted to keep the conflict between the Federation and the Klingon Empire alive, afraid that they would lose their positions as the two began dismantling their defenses.
Certainly those are cases when conflict led to some very entertaining and intriguing plotlines.
But in ST:Enterprise, I couldn't help but notice that the entire "enemies that want to destroy the humans" idea was taken in the opposite extreme, and became the only plotline. Suddenly, the evil villains started showing up everywhere. The peaceful ones became the exception.
Gene Roddenberry had said that most aliens, who had advanced enough to interstellar travel, had also advanced beyond war of any kind. A good example of an excellent and intriguing plot line without conflict is the episode "Shore Leave" from the original series. It takes a simple notion of an amusement park and extends it quite nicely.
In that case, the story wasn't about a malevolent enemy, but rather a simple misunderstanding on both sides. It was a very enjoyable episode. Also, "The City on the Edge of Forever" was another good episode that didn't include an evil alien trying to kill people.
You're right, though, that there is a place for evil aliens in Star Trek. There is also a place for evil friends, too, as in the case of ST:VI. Put all together, it leads to a richer experience for everyone. The point, after all, is to indulge in some entertainment. And Star Trek, at its best, was definately very entertaining.
