I'm against using our Valyrian dragons too, my point is that if getting the seed material from our Valyrian dragons don't kill them, then getting the seed material from a captured Brine dragon don't hurt it either, which mean we might as well, see if we can't also get a minion out of the Brine dragon.
Whether that's by feeding it to Yss so he can make us a Snake dragon, or by sacrificing it to the old gods, so they can make us a Zomok I don't really care, but seeing as once we have captured the Brine dragon, all making Brine dragon material cost us is a bit of money, I'm against turning it into materials, if we capture it alive.