No. Revenge is fine, and the end sometimes does justify the means, and it is sometimes ok to take things into your own hands. But in this situation, a gang wouldn't be the best idea. For one thing, it's not as easy as taking a load of baseball bats and 'having a go'....it would be very, very messy, and as you say, could get very out of hand - a bit different from the old fashioned 'give em a a slap'.

Far, far better would be to find out more about the attatcking gang...have them followed, find out where they live, drink, who their family are etc....and plot revenge at your leisure.