From the first day I received my driver's license (at the ripe old age of 17--hey I wasn't in any hurry!), I have always been an organ donor. But a vegan colleague of mine recently confided to me that she is not. Her thinking is that donating one's organs could mean sustaining the life of someone who will continue to hurt Nonhuman Animals by eating, wearing, or otherwise using them.
I consider if my brother or my mother needed an organ to survive and they were denied because they weren't vegan, I would be devastated. With organs so limited and the demand so great, every organ counts...every organ is a matter of life or death.
Another consideration is that Nonhuman Animals are often killed so that their organs can be harvested to save a human life. I would much rather pass on my unneeded organs that would otherwise be cremated and spare a pig or a monkey.
Often, vegan advocates mistakenly grant far more agency to people than is appropriate. Yes, we all have "choice" and "free will" to some extent. However, most of our choices, behaviors, and attitudes are directly dependent upon structural conditions. Just as it is improper to blame women who become sex workers or stay at home moms and just as it is improper to blame poor persons for being poor, it is improper to blame nonvegans for consuming Nonhuman Animals. Industries that exploit Nonhuman Animals and benefit enormously from speciesism have a massive amount of wealth and power that they are able to apply to all major social institutions: the state, medicine, education, religion, etc. They are able to draw on huge subsidies and externalize costs to drive down the price of their products. They are also able to squeeze out the competition, skew the science on nutrition to their favor, and manipulate public knowledge with intensive advertising.
I suggest we focus on the structural changes and not over-analyze the individual-level moral conflicts. Building a social structure that is conducive to ethical choices, especially for disadvantaged persons living oppressed themselves, will be the best bet for reducing harm against other animals and reducing moral conflicts.