Do you mean those Hanes 3-packs of white T-shirts? Those are kind of thin, usually.
If you're talking about more solid ones, that come in various colors, sometimes with designs or print on them, and are usually a bit more baggy, I don't see what anyone could object to. (unless they were old & thin, too tight, or had vulgar messages on them)
A loose-fitting T-shirt is quite modest. It would go well with a denim or other skirt, especially if you're going to be working/playing outdoors.
Not every woman can find (or make) affordable dresses. Skirt/shirt combination is much more reasonable to come by. Especially depending on the woman's figure.
We can't expect women to wear their nice "Sunday" clothes 24/7. That is simply too expensive.
Unless the man is wealthy, of course. You know -- someone who aspires to live in the city, make 6 figures, etc. We have someone like that on CathInfo, and he doesn't get along very well with Telesphorus.