It probably isn't fair to compare babies vs dogs... for many reasons. But I think disposable nappies are a massive issue. It is the gel which makes them worse. Reusables are great these days and I think they have become really mainstream recently.
Dogs will need poo bags their whole lives, so up to what? 15 years? When do babies usually stop needing nappies? Usually somewhere between 2.5 and 4 I think. But seeing as there seems to be no good solution for dog poo and there is a pretty good solution for nappies (reusables without tumbling them), I don't know which is 'worse'.
But, whatever way you look at it, both disposable nappies and dog ownership are luxuries I think we should give serious thought to.
I know someone will say, having babies is a luxury too and that's true. But if I were to forgo ever owning a dog, so that someone could have a baby, that would be an easy sacrifice / no brainer. I know some people GENUINELY value dog lives over human lives, but I am not one of those people.
Overpopulation of humans is such a big issue too, but seeing as people in places where everyone consumes a lot less, a large family uses less than one, single, childless westerner. So, if we all used less, especially giving a bit more thought before we buy loads of stuff we don't need, there would be enough for everyone as it stands. And that includes pet ownership. Like it or not, it's something we will need to think about cutting down on.
We should also curb population growth too btw, as we already have in the UK. We are already at below replacement birth levels here and actually, there are some concerns about this. The other thing to consider is that we are all living very long lives here now, (some people, including my late GM who died aged 94, would say TOO long in some cases).
Sorry, I'm totally waffling here, but this question has made me think!