I often think that such situations are difficult to reconcile if a 'personal bad experience' has provoked the question. ie if was the questioner's infantry or cavalry that got butchered the rule must be crap. Hardly objective. Mark and Ray you both get it
but alas many gamers do not.
As my old boss once said to me
"Barry, I can make this simple but I can't make you understand it!"
Many people tend to think in absolutes and black and white.
What IS actually happening during this action? What are the toys simulating?
200 cavalrymen wantonly butchering 400 passive, cowering infantrymen huddled in little heaps on the ground, rather:
A disorganised infantry unit who have failed to cohesively form or fix bayonets or have let off an ineffectual volley at too long a range and are now in no position to offer spirited resistance. Some men will lie down and play dead, some will take cover, some will simply try and avoid or ward off blows, a few(but not enough) will fight, draw hangers, swing musket butts or throw stones.. but not enough!
The cavalry charge destroys the infantry unit's integrity and it ceases to be a reliable, directable battlefield unit. It is the same EFFECT as all of the men being dead but not the same THING!
I have written before in articles about the implausibility of wargaming 'casualty levels'. Most mirror armageddon. That was a very rare thing in real life with perhaps the exception of some WW1 & WW2 annihilations.
Casualty rates including ratios of killed to wounded are extremely interesting data and for Saddo like me just as interesting as nice uniform plates