The danger of boy/girl indecency is far greater and far more serious with far more tragic consequences and a potentially far greater sin than the potential for loshon hara via telephone.
OK, so let’s up the stakes…
If you start allowing girls and guys to drive, it will lead to injuries and fatalities. No, not in every case; maybe not even in most cases. But it will happen, and that is why the rabbonim shlita are resolutely and vigorously opposed to it.
Wait, what… they’re not? 🙂
The Wolf