I discovered that a couple of my towels apparently got treated with fabric softener at one point: they have lost all absorbency (I never use softener but apparently someone in the household did). It is impossible to dry anything with them, they just push the water around.
What’s the best/easiest way to remove the vile stuff without damaging the towels?
Fabric softener isn’t going to kill your towels’ absorbancy with a single wash. You’d have to use fabric softener every wash for an extended period of time to achieve that
but what if they used a lot, like an idiot.