Why is leaving seen as a good thing?
Very simply the arguments is that the UK would regain Soverignty that it had to give up so the EU could make laws to regulate the common market and have free trade and economic integration within the EUs borders. Virtually everything is an extension of that.
One of the big ones is the fear of immigration that comes from having the free movement of labour and this is a major argument from the right. This seems to be producing a lot of support for the leave side right now. Another part of the rights argument is the EU legislation is simply "red tape" and therefore makes businesses inefficient or the costs of EU membership versus trade Benifits.
The left would argue leaving would mean we are no longer committed to austerity as part of EU fiscal rules, the dubious reality that a free trade bloc probably cannot be reformed for social justice or progressive ends and that we would be a signatory of the divisive TTIP trade agreement between the EU and the U.S. However the "left leave" arguments have not received much attention in the media.
I will probably vote remain as the likely short term effects of a "brexit" will produce an economic shock, stock market turmoil and probably a realignment in the government further to the right. It could cause serious problems within the UK itself because Scotland is strongly pro-Europe and may demand a second independence referendum if we leave the EU so it stays a member. There is also a vague threat that it could lead to the break up of the EU with the rise of the far right or may restart problems in Ireland (If the UK left the North would leave with us whilst the south would be independent and in the EU so we would have to close the border and that could create tensions there)
If it were a safer option I might vote to leave on the lefts issues but it is a very vague and long term set of objections that may only look good on paper.
But it's a right ******* mess either way with both sides low on exact details, a lot of scaremongering and a fair amount of blatant lies. You have sites for fact checking what is being said. MPs in Parliament have threatened to resist a successful leave vote as the referendum result is not binding- so right there is a constitutional crisis waiting to happen. Even if we stay in the EU it may be ugly with the current PM being forced out, etc.
Donald Trump also plans to visit the UK in the run up to the referendum. I can only guess what that will do to the result. Yikes!