I don't support this. Safe cheong is just a make up term, it is not like the customer will ask for the cert from the prostitute. If he really ask, will the customer cancel his intention if no cert given. In one way legalise this also mean legalise triad activity as most cheong services are related to them. And people still going to look for cheaper option.
There is religion reason as you said, but have you ever consider the woman support on this. Will your mother, sister, gf and wife going to give a nod on this? The one that support this is men, but I don't think this men going to say okay if his wife or daughter said they want to be a prostitute.
Would you support regulating the sex industry?