Yes, it should be legal.
The arguement that forcefeeding ducks/geese is a detriment to their health is a laughable arguement, considering that they're being bred solely to be killed.
The means of making it aren't great, but then again, if you're going to ban this, you'll probably wind up having to ban every single meat on the planet for the same kind of cruelty concerns.
The argument that "we kill other animals, too" doesn't fly. We don't force-feed any other animals to the point of their stomachs exploding, either. It isn't about being detrimental to their health, it's about the torture aspect.
I will admit that it's a fuzzy logic argument with no absolute line, but isn't everything? (If everything isn't, then you're using fuzzy logic to say so... ha!)