One of the problems of mountain biking is you get overconfident. And overconfidence hurts. Literally. Its the same as when you drive in a Mercedes and the way the car hides the road and engine noise, isolates you from the road, you start to feel sheltered and safe right up until you hit a truck head on. In an MTB you think "I have disk brakes and decent forks, I can handle things".
Only you can't, not if you are not paying attention. Question is: if you have body armour, including knee pads, should you wear them to reduce the damage when you screw up? Or will that make you even more overconfident? And how will drivers react to you kitted out so aggressively?