Why (useful) quantum computers probably don't exist:

1

Superimposed quanta don't scale, hundreds of interacting superimposed quanta would require larger internal state than there are atoms in the universe. Mind-boggling. Probably not real.

2

superposition is super fragile, nature tends to determine "random" outputs instead of keeping things in superposition for a long time.

3

Noise, quantum operations are fuzzy to begin with. It's more like nature implementing a very good random number generator than doing complex exponential calculations with superpositions.

Proof me wrong!