It's nothing to do with catholicism. Anyone who actually thinks seriously about it independently of all the political baggage knows damn well that human life begins at the point of conception, since anything else is just nonsensical. And, once you have accepted that fact, all your subsequent rationalisations must surely be made on that basis?
Except of course in purely cold, hard, scientific terms it definitely is. There is literally no other logical point from which you can determine the beginning of life than conception - which is why it's called conception, of course.
What I find interesting is how those who choose to argue otherwise - who would normally consider themselves to be rational and non-religious - start adopting quasi-religious ideas about when life truly begins when it comes to this issue in order to justify their position.
No, I'm afraid I disagree. 'Human life' is a very nebulous concept when applied to a foetus. It isn't complicated because people don't think about it seriously, it's complicated because it's complicated.
And I haven't even gone down the 'what does human life have to do with the debate and why was it introduced in the first place?' line.
It's complicated because people dishonestly try to hide from the brutal truth of what is being done - namely the termination of human life. Once you remove that dishonesty and obfuscation from the equation and treat it as a brutal, purely utilitarian proposition about the value of one life in relation to others, many of its complications fall away.
And the reason we introduce human life into the debate is because a/ that's what's happening here and b/ the right to life or its obverse the right to take it are pretty fundamental ones when it comes to questions of law and ethics.
In which case a person in a vegetative state without any active brain pattern is also a 'human life' and turning off the life support system is the moral equivalent of murder.
See how easily it gets complicated? The human life angle and conception were introduced because of the Catholic church's opposition to abortion. It isn't in anyway disingenuous or dishonest to question the definition of human life and argue that because it is impossible to define it therefore has no bearing on the argument.
Much of that confusion you mention goes away if that is your perspective as well.
No, I'm sorry, but the significant difference here is of potential. The PVS victim has reached a point where life in terms of their brain activity has to all intents and purposes ceased and they can only be sustained artificially. They have no potential for improvement and are alive in name only. When you turn off the machine, nature takes its course.
An embryo, by contrast, is full of potential and to end it is to snuff all of that potential out by a deliberate act of killing. The two are qualitatively different in both ethical and medical terms. One is entirely justifiable in moral terms, while the other is highly morally dubious.
You seem to think that I'm arguing from a position whereby all human life is innately sacrosanct. I'm explicitly not arguing that. I'm arguing that we should acknowledge first of all that we're ending a human life and then work from there.