Although they are of little consequence to major film studios, age ratings are an unnecessary financial hindrance to the British film and video industry. To have material rated by the BBFC (a mandatory step), companies – regardless of their size – must pay expensive classification fees.
I myself am a freelance DVD producer and editor, and I've worked on DVDs of Polish arthouse movies for the US market. Most of my work is with overseas companies, because the smaller size of the UK market combined with the death-blow of the BBFC fees make it not financially worthwhile for UK companies to take risks releasing niche material. Consumers nowadays expect films to come packaged with audio commentaries, interviews, trailers, etc. – and each one of these must be rated by the BBFC at considerable expense, which is enough to completely wipe out any profits made for a small company. This ultimately results in less work in Britain.
Those are just the financial issues. The condescending censorship angle needs little explanation.
Lastly, the ratings are irrelevant now in the age of internet video.