You’re not “taking advantage” of them anymore than they are taking advantage of you. Why wouldn’t you engage with a system that directly supports RMT? So that you aren’t directly supporting RMT?
The fact that something is unavoidably bad doesn’t mean you shouldn’t (and more importantly, Blizzard shouldn’t) continue to do everything possible to stop it, and it doesn’t mean that there aren’t huge degrees of variability in how badly that RMT impacts the game. When talking about individual items for billions of gold (and 1billion is a VERY low estimate, for anything remotely good), we start talking about what takes a legitimate player many, many hours of farming to achieve.
1 billion gold is something like 20 turn ins of whispers, at a very generous estimate. Many items are going for 10s of billions of gold - at 20billion gold, that is something close to 400 whisper turn-ins.
The impact of RMT on D4, especially now in S4 where the cost of masterworking is so high, is insanity.
Edit: To be clear, I don’t “blame” people who choose to trade; it’s insane that the only options are “dont use the system” or “use the system and unavoidably support RMT”. The blame is on Blizzard for not doing nearly enough, nearly fast enough, to ban extreme and obvious volumes of gold transfer that cannot possibly be accrued legitimately.