Some people don't have the gift of gab, or the ability to persuade others effectively. That doesn't make them evil though for using the tools at their disposal.
If that tool is literally magically dominating their mind and compelling them to act as you say, simply because it seems too hard to convince, reason or intimidate them to make the choice you want through other means... and your character doesn't see that as an evil action... then I'm sorry but yes, yes it absolutely does.
I do agree that the game's dialogue is often lacking and dissatisfying at the moment - but as far as I'm aware, any situation where dialogue can be entered into before a fight breaks out also has non-illithid options present for resolving the situation in a way that means a fight does not break out at all. It may be hard to do, especially if your character is not particularly convincing in social situations... but deciding, based on that, that you're just going to take the easy way out, and steal someone else's free will form them, dominate them, and compel them to act as you want, because that's simpler, is absolutely and unequivocally an evil act; there is no question about that, and no dancing around it... if your character does this regularly and doesn't view it as a dark or evil thing to be doing, then I'm sorry, but your character is almost certainly evil.
