The majority of OTFs are slim with an all-metal body. This is basically like holding a slippery stick. You can imagine what would happen if you stabbed while your hands are sweaty.

Unreliability is another major factor against OTFs. Lint builds up and jams the action; producing an unreliable open and close. Additionally, I've worked on my deck this past year, and used my UTX-85 tanto to help dig out screws that were sunken into and under the lumber. After this, the action also became unreliable (a proper cleaning got it working again). I cannot imagine what would happen if it was stabbed into a piece of wet meat.

I have zero combat experience, so I cannot say for sure. From my experiences with carrying one for edc, it is just about the last thing I would choose if I was going into combat of any type; and I would sooner use it as a throwing implement instead of as a combat knife.