Unbiased?
"we can generate whatever distribution of ethnicities, ages, genders you want in your data, so we are not biased in any way"
The moment you specify a distribution up front, you implement a bias (whether or not you're smart enough to recognise that), because your specification is based on your prior expectation.
The reason for random sampling from a real population is that you can't have any prior expectation. Statistics 101.