This is such an emotive subject. Where I live (not mainland England) we have just been debating the 'opt-out' option, and it will become law. I'm concerned people are saying 'the state own your body in an opt-out system'. Surely that's only if (and it's a big if for the majority of people?) you have no NOK? Because they can still go against the presumed consent? (TBH I'd be really cross if my NOK went against my wishes to donate - they know that's not what I want, if anything I've got is useful to anyone else after I'm dead under the very limited rules involving organ donation.)
But I still fail to see how - if you fit the, frankly quite narrow considerations for donation - you can object to donation? The likelihood is actually very slim because they have to be so careful as regards the health of the organs they accept. I have been a blood donor/on the Anthony Nolan register and the organ donor list since I was old enough to consent in my own right. Now, my DC (after a lot of debate as a family) and my DH have also given consent. When any of us die we would like to save someone's life if we can.
We are also Catholics, but see no problem with organ donation. A family member, who was a 40-day-smoker at the time, aged 50 - only has one kidney (she had to have one removed in the late-70s, due to a medical issue no one could have predicted) but is now still alive and well at nearly 90 - no "10 years off her life" here - so thinking the OP's Aunt must have had other health issues if she was given that warning?)
My DCs are adults, but I registered them with their consent when they were under 18. They know what that means. Now, where we live is going to a 'presumed consent' system, but that's fine. Not a moment too soon.
I wish the people scaremongering would stop. I note that no one who is anti-presumed-consent has had the decency to reply to @Foldedenvelopes. Isn't that interesting... nothing to say? Nothing in reply to someone who's been through the hell of watching their child die apologising for the fact their body had let them down?
Frankly, you should be ashamed.
I believe in life after death, for goodness sake, and I've had a donor card since I held my first driving license! When I'm dead, it's not about my body, it's about my soul.