The current system is a recipe for grand hypocrisy and mealy mouthed platitudes ... people seem to have all sorts of squeamish 'principles' and quasi-religious beliefs, right up until they (or a loved one) needs a transplant. Then, suddenly, all the fog evaporates and they are all in favour of donations.
It makes me sick that I have watched friends die because people don't donate something which (by definition) they can have no further use for.
If you don't like 'presumed consent', then there will be many opportunities to opt-out - and that will be very well advertised I'm sure.
Just don't expect to be first in the queue for a transplant if you do opt-out (that last bit is my view, not official policy ... unfortunately)