Make rare items powered by unknown forces

[eliotn]

It will make rare items more useful, because they will be accessible for every class, and it will avoid the problem of making these awesome items unusable for some builds because they are arcane or arcane-disrupting.

[getter77]

This is a good idea, even if it begets the most wonderful sort of slippery slope that I fully support in terms of an Unknown Forces powered class or so...

[supermini]

It will make rare items more useful, because they will be accessible for every class, and it will avoid the problem of making these awesome items unusable for some builds because they are arcane or arcane-disrupting.

Why is that a problem?