Can't we go back to making consumer goods - cars, toys and food manufacturing?
All that would achieve, if the alternative businesses succeeded, is to reduce and maybe put out of business whoever would have made those goods if competition hadn't increased. Similarly, all shutting down the UK arms manufacturers would achieve is to increase the profits of similar companies elsewhere.
In short, all this would achieve is making the world a little poorer than it otherwise would have been, due to the temporary disruption, with no long term effect on the supply of goods of any type.