tl;dr - no-one knows anything, it's a massive leap of faith. So essentially it's an emotional/idealogical issue rather than one of economics.
That said, as the author points out - it's hard to see the UK have more clout in international economics as an individual state, rather than as part of a bigger union. We'd just get walked all over.
I think @andyp reposted this article on Twitter earlier - for the Standard it's actually pretty good: http://www.standard.co.uk/comment/comment/anthony-hilton-stay-or-go-the-lack-of-solid-facts-means-it-s-all-a-leap-of-faith-a3189151.html
tl;dr - no-one knows anything, it's a massive leap of faith. So essentially it's an emotional/idealogical issue rather than one of economics.
That said, as the author points out - it's hard to see the UK have more clout in international economics as an individual state, rather than as part of a bigger union. We'd just get walked all over.