Honestly, I am not sure you will find much good historical evidence or support for it. It is true that there are several examples of historical altars at which celebration of Mass has been mostly or totally facing the people. Oddly, the most famous altar in all of Catholicism, that in St. Peter’s, is built in such a way as to all but necessitate versus populum celebration.
But for the majority of the Church’s history probably upwards of 99% of Masses have been celebrated with the priest not facing the people, that is, facing East, either literally or “liturgically,” even if the altar is freestanding.
Most of the modern infatuation with facing the people at Mass is just that, a modern aberration, all things considered, historically-speaking.
If you want to defend it, go right ahead. But to me it seems difficult to do so given the fact that versus populum celebration was an extreme minority for almost all of recorded Church history, both in the East and West, and randomly popped up in the latter half of the 20th century from pretty much nowhere. More than that, the reasons given for doing so have mostly been proven to be utterly false or, at best, half-truths.
My own theory as to why it suddenly became all the rage is that (1: freestanding altars–a genuine part of Western Catholic history that has been quite widespread in various parts of Church history–became fashionable again) combined with (2: the modern anthropocentric tendencies in society at large that were by no means excluded from liturgical circles in the last century) to produce a silly story in the 1960s that goes: “Gee, freestanding altars, those are a verifiable and widespread part of our history, and gosh golly, let’s make this more community-centered 'cause that’s just what’s the thing to do according to the latest research, so we’re going to trash the high altar, stick in a freestanding one, and put the priest on the opposite side of it.” It is true that there are 20th century examples of versus populum experiments before the 1960s, but these were just that, mostly experiments. However, I would like to do my own research on this.
If you or someone you know of has written or will write an original essay justifying this admittedly odd historical development, I would like to read it.