The lethalty of modern weapons systems and the communications exstant that help control them would preclude it's use in 99% of all situations.
The primary mission of Cavalry (even today) was/is reconnaissance and security of the force. Certainly after the perriod of the late 18th ce. This as it's nature suggests... requires flexibility....mobility and above all speed....over multitudinous terrain and weather conditions. Horses can't do that anymore.
They really couldn't do that in point of fact a 1000 years ago. But they were the best available and hence were the reason they were used. Other tactical combat missions that can be conducted by cavalry can only objectively be analylized with that in mind and how ongoing tech either supported or precluded or substituted their use.
otoh you can eat a horse you cant eat a helicopter or armored or wheeled reconn vehicle.
If we ever return to the days of 1800.. from a tech perspective..then your back in business.
Edited by Centrix Vigilis - 18-Apr-2011 at 17:10