Ok. Here we go.

Do you think all that separates the Daywalkers and the NIghtwalkers could really just be a choice? I mean, it is possible, but it also seems more likely that there would be something... tangible. And while it may not be just one thing that makes the distinction, it also seems reasonable that there would be some things that would make you shunned very much by one group or the other. Nor am I sure how valid your example of the children are. If these two sides hate each other as much as we have laid out thus far, wouldn't children between Daywalkers and Nightwalkers really not be a... thing?

Because I do think that varieties within the species are a grand idea. And I'm all for avoiding generalizations like "always" and "never". Which means, maybe, a choice would be a thing. But it seems to me like the choice would kind of be like a white child from the pre civil-war time period choosing to go live among the slaves, or a black child being adopted by a white family. There are certain cases where certain things just... don't happen, right?