[..]The main argument that I would put forward is that the process of consent still applies here. You need to make a decision to donate when you are alive and sound of mind. There is still very much a choice to make. The onus has now shifted to the individual to make an active decision not to donate.
And the main argument I would put forward is that lack of active resistance is not consent.
The dishonesty annoys me and sets a dangerous precedent. It would be safer and more honest to acknowledge that consent is no longer required.
If the goal is to get consent from more of the unknown (but not very large) number of people who would consent but haven't done so, the safe, honest and ethical way would be to promote registering that choice. Put the choice somewhere that almost everyone will encounter it. Driver's license. Forms for registering on the electoral roll. Forms for registering with a GP. There are options. If the goal is to really push it to the max, make it mandatory to register that choice. Here's a form, you must fill it out. Same as is done with census forms and suchlike.
Removing the need for consent has no advantages over those approaches and is harmful whereas those approaches are not. It's unethical and that's particularly nasty in a profession that is so strongly geared towards maximising benefit while minimising harm. Do no harm? Promoting the idea that lack of active resistance is consent is harm. Promoting the idea that the authorities own people's bodies is harm. And it provides no benefit that could not be provided in a way that does not do harm, if it provides any benefits at all. It's just plain wrong.