Brexit - good or bad?

Following the announcement yesterday by the PM that a deal is going to be struck about the UK's postion in Europe, the media were all over it trying to determine whether it would benefit the UK or not. The key question for most people in industry seems to focus on the debate around the political and ecomonic case of staying in the EU and/or is it better to leave. To us, as a business, the case for leaving has at this point no substance, as to date no economic case has been outlined to state that GDP or the UK's balance of payments will benefit from a Brexit. It just appears at this stage to be a protest movement. 

The world is intrinsically linked by trade and trade agreements and so why change it? The PM is right to push for EU reform but even that must seem like trying to run through mud. Still some reform is surely better than no reform at all.