Fortunately for me, I catch enough fish using 1 rod at a time to satisfy my fishing addiction, so it's a non-issue. IMO, fishing with 2 rods is just too much hassle anyway, whether legal/ethical or not.

For example:

Trolling - One rod goes off of the downrigger and you not only have to fight that fish, but you have to pop the other rod and crank in both 'riggers, or risk getting all tangled up and losing your fish.

Casting - Who can cast and retrieve 2 rods at the same time? This I'd like to see.

Plunking - Again, one rod gets bit and it's a Chinese fire drill trying to keep the fish out of the other line.

For me personally, even if it WERE legal to fish with 2 rods simultaneously, the above scenarios would make it too stressful, and one of the main reasons I fish is to relieve stress.