We should not touch caches belonging to others as there is a chance that they have withdrawn the cache from listing at geocaching.com but still list it elsewhere.
Groundspeak has no authority legally in the UK to remove a physical cache or to encourage others to do so, their authority goes as far as listing or not of a cache on the websites under their control.
I support the principles under which Groundspeak works but until it has a legal standing on which to instruct removal of caches in the UK it shouldn't even consider a scheme to remove caches.
We have enough issues about caches being stolen this could develop the same way.
Lets give this a 100% miss.
Paul