Right up until the point it's no longer your own body because you're dead, yes.
> To take it to extremes, should the government be able to take “spare” kidneys from live donors?
No, they're not dead.
> Should criminals be forced to donate blood?
No, but again, they're not dead.
> What about children that die in child birth should they be harvested for organs too?
The law only covers adults with the opt-out which would make this another no.
> Where does the line stop?
Pretty much exactly where the law says it does - "All adults in England will be considered as having agreed to donate their own organs when they die unless they record a decision not to donate (known as ‘opting out’) or are in one of the excluded groups."
[edit: Missed the A in "All"]
No, and that's the point. When you're dead you cannot have agency over your body even if you had the right to.
I find it weird how people compare this to the government treating them like a "bag of parts", as if they were more than a rotting corpse at that point. If you have a religious belief or some other reason that makes you think otherwise then go ahead and opt out, I don't have an issue with that.
> To take it to extremes, should the government be able to take “spare” kidneys from live donors?
Who ever asked for that? If the time came where the UK government started acting like the CCP the law today wouldn't matter either way.
And it’s not like it is forced, especially with the family being able to “stop” it even when it happens. The status quo was a different tradeoff.
I believe the answer is somewhere in-between. We certainly don't have full agency over our own bodies. Can't take the drugs you want or need without asking permission, you're highly encouraged to stay healthy, vaccinations are mandatory, suicide is highly discouraged.
As always, it's a trade-off between the individual self and the society we live in.
Do we have agency over our own bodies or not?
How can I keep that agency and help someone under an opt-out system? That has been taken from me when better, workable opt-in solutions weren’t tried.
To take it to extremes, should the government be able to take “spare” kidneys from live donors?
Should criminals be forced to donate blood?
What about children that die in child birth, should they be harvested for organs too? ‘Cause the NHS were doing that at one time.[1]
Where does the line stop?
1. http://news.bbc.co.uk/1/hi/1136723.stm