Let me tighten the frame first: the biggest threat is the one that destroys the process, not the one that biases it. A gerrymandered district still produces a winner both sides accept as real.
My opponent's strongest point is that safe seats feed denial, and that's fair. But fuel isn't fire. Denial burns legitimacy itself, and it shows up in fairly drawn states too, so gerrymandering isn't the cause. If enough voters reject the count, no map is enforceable at all. Gerrymandering's fixes take years, yes, but at least a map exists to redraw.