ww1/2 troops could and did take charges, everyone was still supplied bayonets and drilled with them... no idea what the sitch is today but automatic weapons and indirect fire probably make an already narrow use-case nigh nonexistant

i would contend horses are cheaper than most military vehicles and were done away with for valid strategic and tactical reasons, not cost. according to this a horse was 4,000 some today bucks in ww1;compare $220,000 for a Humvee. the comparison is more stacked with proper armored vehicles. they were trading oats and veternarians for brand new factories & loads of mechanics & shittons of oil.

but its a good trade. mechanised can directly engage, move faster for longer, and haul more shit. the areas nontraversible by a military vehicle but fine for horses is very narrow and there's still places only infantry can get. you did touch on horse casualties---indirect fire means you can't have your horses anywhere near a proper fight, which basically makes cavalry faster infantry thats quieter than other options