I figure the more time a wheel of a vehicle spends in contact with the surface the more safe the vehicle is. There's also an issue of longevity of critical parts and if you have something designed to absorb stress you can improve it. In the end there's common sense - "soft" is strongly correlated with "safe".

I think disc brake disadvantages are common knowledge. And so are the advantages. I just envisioned myself mostly on the "con" side of the list...

Yeah I exaggerated a little, sorry. Fitness is not the whole point.