I've never bothered to research the cons, so perhaps I'm just ignorant on this topic, but I personally can't fathom why someone wouldn't want to be an organ donor. Mind you, I'm not religious and want to be cremated, so maybe that factors into it. But without trying to be too judgmental given my own lack of research on the various angles of the topic, people who are against organ donation always come across as ignorant pricks to me.