Via Megan McArdle, we find a commentary by Dan Drezner on the limits of constructive engagement:
Put crudely, if a regime wants to stay in power at all costs, all of the economic openness in the world is not going to make much difference, because the government that wants to stay in power will simply apply strict controls over trade with the outside world.
But a repressive regime will do more than "apply strict controls". It will bring in the products its ruling class wants. It will apply tariffs to raise more money for its own ends, or else will allow bribe-collection along the delivery chain to create revenue streams which can be directed to supporters.
The point of sanctions against, say, Iran would not be to isolate them from the Western world -- they are already seeking to isolate themselves. Rather, it would be to deny their rulers the ability to cherry-pick the West's offerings, and to give them one less way to buy off potential dissenters. To argue that sanctions strengthen the Iranian government is demented: it ignores the fact, pointed out by Mr. Drezner, that that government could duplicate the favorable effect of sanctions internally. And, without sanctions, it could make a pretty penny doing so.