David Friedman quotes Adam Smith:

No discipline is ever requisite to force attendance upon lectures which are really worth the attending, as is well known wherever any such lectures are given. Force and restraint may, no doubt, be in some degree requisite in order to oblige children, or very young boys, to attend to those parts of education which it is thought necessary for them to acquire during that early period of life; but after twelve or thirteen years of age, provided the master does his duty, force or restraint can scarce ever be necessary to carry on any part of education.

Compulsion is bad because superfluous.  But an “anonymous” commenter prefers William Godwin, because he goes further.  Compulsion is bad because bad.

Let us consider the effect that coercion produces upon the mind of him against whom it is employed. It cannot begin with convincing; it is no argument. It begins with producing the sensation of pain, and the sentiment of distaste. It begins with violently alienating the mind from the truth with which we wish it to be impressed. It includes in it a tacit confession of imbecility. If he who employs coercion against me could mould me to his purposes by argument, no doubt he would. He pretends to punish me because his argument is strong; but he really punishes me because his argument is weak.

Sadly though, compulsion can work, at any rate to the satisfaction of those doing the compelling.  If all it did was achieve the pure opposite of its purpose, it would surely not be so prevalent.