it matters at the point when you choose to build a business on the method of accessing a 3rd party service.

Why? They are having to pay them and then buy your services for data entry. This is no more unethical than hiring someone to do your banking for you.

Violating an EULA by doing this may be unethical, but in that case, it is violating the EULA that is unethical, not the general practice of providing a new interface.