Are backyard repairers dangerous?
Yes it is dangerous. How many unsuspecting families with infants are driving around in cars that have shonky repairs done to them?
There is enough evidence that cars that have been repaired from structural damage incorrectly can make the difference from death to survival even in a medium speed impact.
Backyarders, seriously the major issue is not about their safety or waste disposal. The major issue is that all repairers are done to the minumum cost as possible so at the sale of the car a maximum profit can be made. I have seen used cars with cut/shut jobs (half original vehicle, half stolen??), cars with chain marks around its chassis rails from trying the dodgy way of straightening the body and poor welding and rust around badly repaired supports, X members and chassis.
Backyard panel beaters are another form of leeches, most on the dole or on compenstation that make decent tax free money at the expense of safety to the unknown buyers.
More reason it pays to get any used car inspected before purchase.
Personally I think that the sale of whole smashed or written off vehicles should be illegal to all but licenced repairers, this will cull down the number of dodgy backyarders.