Here is my guess based off of everyone elses hard work and thinkin'....
I think getting the soul back might be worse....it punishes both the human and the vampire. The human, if he/she is good, would be left like Angel with guilt over what he/she had done. Meanwhile, If my guess is right from what Angel said in season two's "Dark Age" the demon is stuck in a 'limbo' with a view, seeing everything that the goody two shoes mortal is doing (they are stuck inside) and having no outlet for havok....similar to the behavior that can be forced on the monster by a chip, but with double the punishment of regretted actions brought on by the curse and its effect of the 'persons' memory of what they had done as a vampire.
If, like some have allready said, the soul is just as wicked as the demon, a curse is not a punishment at all, short of a blow to the monsters ego. Yet, that would still be a punishmet, at least on some level. Since the demon would be second fiddel to the human- well, as long as it is aware of that, in a way I think thats still a punishment to the vampire, and kind of like being in jail.
The chip still leaves the deamon with some amount of control, although the intent is to modify the behavior, unlike a curse where its getting its essence displaced by the very soul it once enslaved/replaced ; It is denied of any control at all, and is left powerless.
Also,I'm not sure the chip would be double punishment (although I'll admit the whole limbo with a view is just a guess, might not be double punishment either.) When Angel gets his soul back, he doesn't remeber all the bad things he's done as Angelus right away. If a vampire gets chipped he's still a vampire, not this duel soul thing. The human side is not really there, thus no double punishment.
Thats why I'd never mess with a gypsy, they aren't concerned with justice or behavior modification, the just want to bring the woe untill you say whoa...and then they still keep bringing it.