You really can't compare a style as generic as "karate" with really anything, nevermind kickboxing. You have to be more specific as to the type of karate being done -- not necessarily a specific style, but at the very least broken down between limited contact vs. no contact vs. full contact. The main advantage a kickboxer (I mean a contact kickboxer -- not necessarily Muay Thai, but definitely not cardio-kickboxing or some other non-contact stuff) would have over a "generic" karateka would be twofold: 1. They are used to being hit 2. They are normally in superior condition (not always, but normally) If the karateka in question studies a full contact style (say kyokushin or one of its offshoots, like enshin or ashihara), then the comparison is not as clear cut, as those karate stylists train remarkably similar to how kickboxers do. However, if the karateka is a light contact point fighter, or a tag fighter, then they may not be used to being hit, which would prove to be a serious disadvantage in a combat situation.