You don't have to assume murderous intent to find a reason to be against organ donation, just look at their attitude towards the value of your life and your body. Wanting to give up your own flesh for the benefit of saving lives might be a virtuous and benevolent impulse, but it's safe to say the the institutions which try with all their might to coerce you into taking dangerous untested drugs, and are happy to deny you lifesaving treatment if you don't, do not share that same respect for life and certainly not for yours.

Until the last 2 years I was something of a 'muh science' guy and I idly thought that one of the cool things to do with one's body after death would be donate it entirely to a research institution, to do with what they wanted. Nowadays I realise this is the equivalent of donating it to a travelling clown show which poisons its audience and mutilates children backstage. Anyone enquiring into my organ donation status will be laughingly told to fuck off.