Even if you can think up good reasons for it...it will never be legalized because too many people find it repugnant, or morally wrong...I would also say the idea of letting people go into morgues isn't going to work out, like any meat, I would think that you would need to cook it and try and preserve it so it dosen't go rancid, or have any of those other nasty side effects bad meat can have.
Also, the first thing people are going to bring up is the human rights issue...I mean, how many people would really want to be eaten by another person after they have died? Not many I would think...so that also would put the brakes on legislation to legalize it.
Oh, and lets not forget the religious aspect. Most all religions would frown upon cannibalism, and this is also gonna hurt public opinion towards legalizing it, and public participation should it be legalized.
The fact is, like marijuana, or drugs, or any of these other controversial things that you might be able to make a rational case for legalizing, the public has been so trained to reject it, that there is no way a politician would even suggest a law on such an issue, let alone get enough compliance to have it passed. Nobody wants to commit political suicide on something they know will never get passed anyway.