Absolutely! I think everybody has the right to make their own choice about their own body, even in death.
I don't think that people who choose to do a good thing like this should be respected for their choice, but I don't think that people should be shamed for choosing otherwise- even if their choice seems silly.
Organ donation is a great thing and I wouldn't want anybody making their decision against it based on any false ideas, myths or misunderstandings, but as long as somebody has thought about their choice and is happy with their own decision I think that's what matters.
I would encourage anybody who has made the choice not to donate to have a look at how the process works, the amazing things it can do for people's lives and have a think abot how much their dead body will mean to them compared to those amazing possibilities (especially considering the normal processes that happen after death anyway). But at the end of the day I think it's important to respect that it is their choice.
And hopefully everybody here will have a long long time to think about their choice and potentially change their minds anyway!
I think it would be nice to know some people's reasoning for either choice if they are happy to answer, but nobody should be pressured to answer if they don't want to.
Personally I was uncomfortable with the idea to start with, but decided that at the end of the day I'm having my body cremated anyway and don't see any particular meaning to my physical form. My tonsils have already been chopped out and dumped in a bin or something and I don't have any more significant attachments to any other organs (apart from them keeping me alive!). So there's kinda no reason for me not to and if I can live on a bit through my contribution to somebody else that would be great.