I think LNT is a principle to strive for. Obviously a fire (even in a pit built by others) leaves a trace. I have a hiking buddy that pretty much won't camp where he cannot build a fire. I think fires are great and love to have a fire where permitted. Fire is a trade-off, if you're practicing LNT, than a fire would be out. If you're shooting to see how little you can get away with carrying...then you're most likely going to have building a fire as part of your plan.