If the knee weren't so difficult to repair and so crucial to mobility, then I could see why it's still allowed. There's a reason that even fighters in the sport are calling for a ban. Sure, until then exploit the shit out of it to get the W. I'm just saying I'm glad it didn't affect the next round that we got to witness with Nate's mobility completely shot. Fighters don't throw this kick just for the points.
You can try to make the argument that it's MMA -- we're watching grown men hit eachother in the face here -- all day long, but by that logic punches to the back of a head, groin, cranking a submission too long, fingers to eyes, etc. would all still be allowed, too.
This strike will be banned, it's just a matter of time.