With overbooking itself, up until the point that someone is bumped against their will, the practice is purely a win-win for all; airlines save costs -- a boon for competition and prices -- and passengers volunteering for a later flight get compensation that they view as valuable enough for the inconvenience.
For involuntary deboarding, there are scenarios -- albeit presumably unlikely -- that can occur, regardless of overbooking, that necessitate its use. For example, as mentioned in the article, sudden weather changes forcing a reduction in weight, or simply a broken seat. Point being, there are possibly entirely legitimate issues of safety, generally outside the immediate control of the airline, that easily trump any one person's right to their seat, even after boarding.
While much blame should be placed on the police here in terms of how they handled the situation, I don't see why this isn't something to be handled, ultimately, by the DoT in further dictating passenger rights. For this specific case, if involuntary deboarding was only allowed, say, for cases affecting passenger safety, the airline would be left with the choice of either, one, living with the repercussions of not being able to transport their crew immediately, or two, upping the voluntary compensation until there was a taker (and there would be at some point).
That is to say, I don't see why this issue couldn't be handled more elegantly by creating a market where the airline gets forced to up the compensation until it is approximately equal to the expected costs of not being able to deboard someone. And if that creates too many scenarios where they simply don't get a taker for the deboarding, then clearly their actuaries need to be fired.