FWIW, I don’t think using a recip mare makes you callous. I would be very concerned for any mare that I bred, my own or a recip.
My mare has more value as a riding horse than a brood mare, and even if she had value as an egg donor that doesn’t mean she should necessarily carry a foal. (Not that my mare is breeding quality, as amazing as she is otherwise). That said, I would vastly prefer to use a recip if I did choose to breed her because she has more value as a mount, she has not to my knowledge carried a baby, she is older, she has known health issues that may make uneventful foaling difficult, and she is my heart. I would much prefer to use a recip with a track record of carrying pregnancies and delivering uneventfully, as opposed to putting my mare at risk.
That doesn’t make me callous, it makes me calculated.
Mare would strongly disagree. She wants a baby very badly (you should see the way she looks at foals!), and is extremely “receptive” to horses of all gender identities and sexual orientations.