Haven't RTWT, sorry, & this might have been said already but..
The flaw in your argument, I think JellieEllie is this:
Anyone who physically harms, neglects or kills their children should not be given a right to have further children. They really shouldn't.
The people you are referring to are not given the right are they?
Assuming that there are no fertitlity issues, this is just something that happens naturally, unless steps are taken to prevent it from happening.
You are looking at it from the wrong angle, I think....If the couple in question, were given unlimited NHS funding for fertility treatment, you could argue that they were in theory being given the right to have more children (even though it might not even work).
This is not what is happening. The right if you want to call it that, is already theirs.
So really, maybe you should be honest, because your argument is factually incorrect and void, as I see it.
If you want to ask "Should these people be forcibly prevented from having more children?" then be honest and throw that one out there!
For the record, IMHO, no, people should not be forcibly prevented from having more children.