The parents encouraged Michael to divorce Terri and give her over to their care. Why did he instead take all efforts to ensure that she not receive therapy? Note that it wasn't until later--after it became clear that Terri wasn't going to die of neglect--that Michael suddenly "remembered" Terri's supposed wishes.
Call it a "conspiracy theory" if you must, but if it looks like a duck, walks like a duck, and quacks like a duck, it's obviously a loving husband, right?
You've got the entire story I see, every last detail, under your blet. You've checked all the facts carefully, you've examined motives, statements, autopsy reports, and you've deduced that they can only mean one thing: cold-hearted, calculated, willful murder for financial gain (not to mention the fun of watching someone close die). Not a bad year's work! Thus, it is society that has failed in recognizing, as a whole, what you have so dutifully discerned. You have clearly risen to the uppermost stratum of moral clarity. Well, except for one small detail: it all can be explained much more readily by coming to a completely different conclusion. Other than that, I'm all for hanging the dude in public. Would you like to pull the lever?