Caporegime
For me the, stay campaign is very negative.
Some of that is simply the nature of the beast. If we were discussing joining the EU campaign then all the benefits of the EU would be positive points that the In campaign could make; but because we're already in the EU many of the positive points are converted to negative ones about leaving.
For instance, if we were campaigning to join I'd be saying "joining the EU would boost our economy by around 4-8% over the next five years" instead of saying "leaving the EU is likely to reduce economic growth by around 4-8% over the next five years". Instead of saying "every UK citizen will gain the right to live and work anywhere in Europe", I'm saying "you will face new barriers to living and working in the EU if we leave" and so on.