I would say we want the questions but not the tag.
Tags are mainly useful because we can watch them to find questions which are relevant to our interests, and which we have the expertise to answer. Arguably some people might be interested in the pros-and-cons Q&A format as a way of learning about a wider range of topics, so the tag might be useful to them, but nobody has expertise in "pros-and-cons".
Moreover, pros-cons cannot work as the only tag on a question, but the tag will potentially be an attractive nuisance for people asking pros-and-cons questions who don't put the effort in to add a content-specific tag. This doesn't seem to be an issue at the moment ─ there are currently no questions with only this tag and no others ─ but it's something to look out for in the future.