Among the rest of the Autobot crew, Mirage doesn't quite fit in. He's a perfectly capable soldier, and even better at espionage, but he's pretty much literally in a different class than those he's found himself hanging around with. It's a little bit like if Lord Grantham found himself fighting a war alongside Thomas Barrow, perhaps with John Bates as his commanding officer.
Part of where that analogy breaks down, of course, is that Lord Grantham is unquestionably devoted to the British cause in wartime (and, indeed, even laments not being allowed to fight), while Mirage is a little less dedicated to the Autobots. Indeed, many of his companions have accused him of sympathizing with the Decepticons! While that accusation perhaps overstates the point, it is nonetheless true that it is probably unwise to trust Mirage too readily. Unlike other characters, the issue is less that Mirage is a pacifist at heart, and more simply that he thinks that fighting a war is beneath him. Obviously, such a attitude does little to endear Mirage to his colleagues.
Mirage is perhaps best-known for the abilities for which he is named, although these oddly differ according to continuity. The cartoon gave him the ability to become invisible, which is undeniably a useful skill for a spy to have. His tech specs, on the other hand, suggest that he can change his appearance or cast illusions for a period of time, which also has obvious uses, and indeed is probably even more in keeping with the name. Of course, this is another case where the cartoon's ubiquity has supplanted the other versions in most people's imaginations.