U = R x I
volts (U, probably 19VDC) is constant. The laptop has a resistance (R). This means that the laptop has already dictated the amount of currents (I) that it pulls. You can connect an 100A charger to an phone. The phone dictates howmuch it actually pulling. There is no battery damage/harm in doing so.
If you charge a battery at full-speed, It can heat up. This is in the long term bad for (Lithium) batteries. That's where the myth might come from?
*fixed formula order