why stop there? lets ban all activity that doesn't produce tangible goods. the number of parasites, i.e. people who consume tangible goods but don't produce them, is probably higher than the number of people who do
fields, mines and factories. we don't need anything else
Material production still requires accounting, installation, transportation, delivery, disposition, optimization. Financial parasitism more clearly occurs when someone pledges something to lenders which they do not actually own. For example in the 19th century when JP Morgan lent to planters on security of chattel slaves, the planters pledged the bodies of other people as collateral. Arguably loans should only be issued on security of personal property which does not deny the personal property rights of others. This might exclude leveraged lending of money on security of money (arguably lending on security of state property) and excess real values due to land scarcity (arguably lending on security of common property).
fields, mines and factories. we don't need anything else