Sorry, I don't buy it. The same could be said for waging war on the Alliance (only the difference there of course is that it is morally right to kill Forsaken).
That's some HMP logic right there that fighting is wrong because you might have to die in a war.
Saurfang isn't a coward.
One of the most important rules of warfare is not to pick fights with people you can't beat, or who will cripple you if you do beat them.
It's not cowardice to recognize a foe you cannot beat on your own.
That's only more reason to destroy them sooner.
I'm arguing it can't be done. The Forsaken are too powerful to be outright destroyed in what would be a three-way war. Everyone would come out of it crippled and broken.
To use a real-world example, US Army doctrine states that any frontal assault on enemy defenses should have at least 5:1 odds in favor of the attacker. This is assuming conventional warfare. Granted, technology is very different between the modern US Army and the WWI-era tech used by the factions in WoW, but look at trench warfare. Even small numbers of defenders with artillery, machine guns and gas could stop vastly superior numbers of attackers supported by artillery. The Forsaken definitely have artillery and gas, and may have machine guns as well. The Orcs also have artillery, and may have machine guns, but most of their warriors are melee fighters, so they'd be even more vulnerable.
No faction in World of Warcraft except the Legion or the pre-WotLK Scourge had the numbers for a 5:1 assault on another major faction, to my knowledge, unless it's something extreme like an entire Alliance army attacking the Blood Elves.