I love the idea there's a debate about whether we/UK should rejoin the EU Customs Union; its the same old entitled nonsense.
Sure we can express an interest or even desire to rejoin, but expressing that in the face of the EU's pretty obvious position that it treats the UK with suspicion & would only welcome the UK back with very serious conditions, is just political stupidity.
If we want to rejoin step one is building back trust & goodwill, something we've not really been doing!