I see a lot of people complaining about the 'fear based' campaign - but I've never seen anyone come up with what an alternative would really look like. It's hard to fight a positive campaign for the status quo, if not straight up impossible. We all know what living in the EU is like, some people like it and some point don't. It's not like there weren't positive statements made about the EU and immigration throughout the campaign, but those statements simply don't play with a base that is distrusting, cynical, conservative, aged, and to some extent xenophobic and downright racist.
There are some arguments where it's hard to run a positive campaign. If the choice is between setting your house alight and not setting your house alight, you can be damned sure that the "Don't Set It On Fire" campaign will focus on all the bad things that will happen.