I am on the register. I have a son who will eventually need a lung/liver transplant due to having cystic fibrosis. I have always been on the register (it's something my mum actively discussed when we were young).
I have always supported organ donation, however having my son makes me actively support it and I'm probably more vocal about it because when the time comes and my son needs a donor, I want to know that one will be available.
Having gotten to know adults with cystic fibrosis who have sadly passed away while waiting, I know how hard that is.
My family was also unfortunate enough for my husband to have renal failure (kidney failure). Being true to my word and an ardent organ donation supporter, I donated a kidney to him a few years ago. It has made an unbelievable difference to our family. My husband was dialysing three times a week and was extremely unwell. He also had two heart attacks caused by the issues of kidney failure. His first heart attack happened when our second baby was just four weeks old.
Our lives are much better since my husbands donation. Yes, we still have my sons cystic fibrosis to deal with but overall our lives are better - we've been lucky enough recently to travel which we just couldn't do before.
I would support an opt out system because I know how difficult the opt in system had been.
However I would always respect someone's decision not to donate, especially if they wouldn't accept an organ. That is their decision to do with their bodies as they wish.
They never take organs from people who aren't properly dead btw. It is always confirmed that a transplant donor is brain stem dead, often arising out of accidents. They try and obtain the organs as quickly as possible so that donors can be placed to rest as soon as they can. It's all done very humanely and not like some harvesting plant where dead people are mistreated.
For those who require more information there is a brilliant website called live life then give life set up by two wonderful women who have been heavily involved in the transplant system.