Sorry if I seemed to be implying that parents who did poly without veto power were irresponsible, Natja. That is not what I meant at all. But I have noticed that the poly activists and those who otherwise write about polyamory a lot online, who weigh in as strongly anti-veto, seem to be either child-free, or else their kids are grown and gone. And that their thinking on this issue is often very, very simplistic.
My husband and I like to make lists. We had always been vague about veto power, just that we saw it as a nuclear option. A couple of years ago we felt a need to be clearer, so we tossed around ideas for what would constitute grounds for veto. That was how we came up with the list I posted here.
It IS true that my husband tends to see the best in people, as I have posted in a different thread here, and to excuse bad behavior. And that I have doubts about his judgement of people and find it difficult to trust in it. So we have veto power, but we both feel it is important to define how it can, and can't, be used, so that our partners are protected as much as possible.
I do not think my husband would ever tolerate continuing in a relationship with a partner who developed serious substance issues or endangered our children. If he did, I can't imagine that veto power would even be relevant, since I can't imagine sticking around in the marriage if that was the case.