Ok what you did was strip out the taper. If the crank arms are going down far enough that the arm is rubbing the bottom bracket, there are two possibilities, both of which sound likely at this point:
1) you stripped the square hole on the crank arm (if its loose and you ride with it, it doesn't take long... also will occur if you over tq the arm)
2) if the BB is loose it may have backed out enough that your crank arm is getting close to rubbing it (hence the slowed rotation when you tighten the arm down)
What you will need is a new crankset and a torque wrench to fix the problem. And don't grease the spindles when you install the new arms.