Sure.
The unified rules that were developed by MMA refs, doctors, etc allow for leg kicks and deem them a legitimate strike unlike headbutts, groin shots, and the like. Prior to mixed martial arts becoming a "thing," leg kicks were still around in individual martial arts and I've never heard a serious argument that explains how they're a dirty tactic at all. As a martial artist, if someone throws a strike of any sort, I suggest you learn how to defend against it otherwise you're gonna get hurt. That goes for simple jabs, heel hooks, front kicks, and whatever else you could possibly think of.
If you take issue with fighters using the rules to their advantage and winning in perfectly legal fashion, I recommend taking it up with athletic commissions and the people who developed the unified rules.