When you consult the people who have done serious research on what the results of a Brexit will be — politicians, civill servants, economists — they overwhelmingly say that the evidence points to it harming both Britain and the rest of Europe. They are not unanimous, but the majority is huge (Evidence below.)
What the Leave campaign has in response to this is Michael Gove’s line “We’ve had enough of experts”. So it comes down to this: for the 99% of us who don’t realistically know enough about economics or politics to have any idea what the result of Brexit would be, are we going to trust experts? Or someone who explicitly does not trust them?
Even if your heart says Leave, your brain should be telling you Remain.
Appendix: some evidence
Ipsos MORI conducted an online survey of members of the Royal Economic Society and the Society of Business Economists. 88% thought it most likely that real GDP would be negatively impacted in the next 5 years, if the UK left the EU and the single market. 4% thought GDP would be positively impacted over the same time period.