Has selective breeding damaged our dogs?

I've recently been researching UK breeds and was shocked to find how rotten they are. Basically it seems to me that every breed has several serious health issues; usually eyes and joints, but also other really horrible conditions of their brain and/or organs that are fatal. Even breeds I thought were solid like terriers are full of rot, and I find this shocking seeing as the UK Kennel Club bangs on about how they work for the good of dogs. The healthiest dogs are mongrels, which tend to live long and be healthy.