Yup, I always wash new clothes (with the exception of coats which would require dry cleaning - I don't bother with that).
If you can think back to the 'oldun' days when we went to a shop and tried on clothes in fitting rooms (a long long time ago...), did you ever accidentally drop something on the floor? Yuck! Many fitting rooms were absolutely filthy and some shoppers will have just dropped garments on to the floor whilst making their selections.
I am not writing of a little backstreet store but major retailers - always dust and fluff on the floor, so yes, I wash new clothes.
As to mail order (the new 'ordinary'), I also wash those as they may well have been in someone else's home before they reached mine and the same applies as to fitting rooms. Just don't know where they have been/who they have been on!