Also conditions in the trenches - from disease, exposure to elements, the smell, the gas attacks were horrible.

On the other hand, being infantry on a modern battlefield? Where a drone, a missile, or computer targeted artillary you never saw or knew was coming can just wipe you out at any time?

Also with helicopters, indistinct front lines, mechanized troops, modern troops are constantly engaged in conflict where WWI and even WII troops outside some very active areas had stretches of calm between combat.

A modern war would be its own version of hell. We saw this when elite Russian mercenaries engaged a use military outpost in Syria and got slaughtered... we have gotten too good and slaughtering each other. The only hope would be that the obscene cost of modern weapons would limit the scale of a modern war.