OK, if you bring in the Catholic issue I totally agree with you - I'm not saying they should have their marriage annulled by the Church, just the legal side dissolved. Net effect - Michael cannot remarry in the Catholic Church. We sure agree there.
From a moral standpoint, adultery is wrong, even if one's spouse is incapacitated.
From the legal perspective, it's more complicated, certainly. His legal marriage to Terri is not stopping Michael Schiavo from living with another woman and having children. And there have been plenty of "kill the wife to marry the mistress" (and "kill the husband to marry the boyfriend") situations, even without the disability issue. No matter how easy divorce is, some people are still going to kill the would-be ex-spouse, I guess.
The big difference in this case, is that the courts are facilitating, instead of prosecuting, the murder.