The long and short of UKARA is this: Not only does it prove your defence and gives retailers the necessity to sell RIF's, but it also stops idiotic 13-15 year olds getting their hands on toy guns to the point a SWAT team needs to be called to a shopping centre.
Though i have heard more negatives than positives: A good retailer of ours WOULD apply for a UKARA/VCRA license, but says it costs £200 a month just to keep it updated and legalised in order sell them. Luckily their relative has a high ranking job with Armex, so we get our gear on a small discount and without the shoddy two-tone.
That being said, UKARA simply over-defines the difference between the gun toting children, maniacs and idiots who think it's okay to walk around with a holstered pistol, with real players of airsoft. Personally, I don't have a UKARA and don't see much point of owning one, but will get one for the sake of it just to make my online purchases easier, wherever necessary.
TLDR: UKARA is the fineline between an airsofter and the possibility of a psychopath.