I have done. I could give several more reasons than you've listed above to support your own argument. That's not the point, though. John's kids are hypothetic

I have done. I could give several more reasons than you've listed above to support your own argument. That's not the point, though. John's kids are hypothetical. But so is John. As is Harry. As is a 500 year old Aubrey de Grey. Rights are what people decide they and others should or shouldn't be entitled to based on a consensus of what most of us consider to be, you know, morally right. If there was consensus on the rights of people yet to live (who may or may not ultimately be born) there wouldn't be differing views on pro-life/pro-choice - and the terms would likely not exist. To come back to the crux of your argument, though - I don't believe our John is any more responsible for a single potential offspring that doesn't come to pass than a father is for every sperm that doesn't fertilize an egg. That would be, as you've said, absurd. My point was that suspending the natural cycle of life in a way that prevents pro-creation is, in my view, morally wrong. Something I imagine we disagree on.