Hmm… are you sure about that?
If you had a weapon with 50% ignores armor, that dealt 60 damage, and the opponent had 60 armor – how much damage would you deal?
It would depend on how effective it was against armour, of course. If it was 100% then the armour would be destroyed and the 50% of damage (30) would be fully applied to hit points, since no armour remains.