I was wondering if the slippery-slope argument really held. There's a fairly simply public-interest argument that could be made against gun ownership (see: dead schoolchildren all over the US), and this argument has been successful in many other countries (UK and Australia have both made firearms illegal in most circumstances).

I don't think you can make the public-interest case against abortion: a very small number of people would argue that mass shootings are a good thing, but it is not clear that a large proportion of people (in the UK at least, the US is a bit of a mystery to me) would argue that the act of abortion does any damage (or at least, nothing like killing someone).