That whole interbreeding story isn't true for the most part, anyway. Nephilim are by no means encouraged, but... the major point of contention is that nephilim are able to do things that a regular angel couldn't. Angels are bound by rules and hierarchies that halfblood children aren't.

So, less powerful, but more of a wild card in the long run. Sometimes they are seen as intermediaries between Heaven and Earth, other times as unnecessary troublemakers.

It's against angelic nature to exterminate outliers, though, so you wouldn't have to worry about that.