Heh, interesting that you mention Motorhead. IIRC Lars Ulrich said in one of the interviews that one of his memories about them was when he went to their concert and saw a punk with a huge colored mohawk that no one seemed to mind (which to him was pretty unbelievable to see for that time). Guess that doesn't always work both ways (maybe unless you're actually Motorhead, haha).
The punks have always been the least accepting between the two groups. They started to merge up in the early 80's then straight edge hit and drove another stake between punks and metalheads. until "black metal" came along with the intensely satanic theme metal never really had a group philosophy and punk had already written quite a few manifestos and was a heavy political and social movement
The way I saw it back in the mid 80's metal owes punk huge for the music but I'm glad most metal never got too socially heavy