But isnt't it very hard to keep morale of soldiers ( especially the ones in the front rows ) high ? In medieval warfare, your life depended upon more or less your skill. But muskeeter formations shooting each other from couple of hundreds of meters, you are almost guaranteed to die. From tactical point of view, why does weaker side opt to use the same tactic with stronger side ? I mean, that tight muskeeter formations doesn't seem to include any strategy, just ranks being decimated at a similar rate.
Actually tight ranks IS a strategy for keeping morale high. Men become naturally ashamed of trying to lie down or hide if all their comrades are standing up next to them, and (as noted below) you can't use a musket unless you are standing up. It doesn't matter if your side is stronger or weaker - if you don't stand up to fight, you can only shoot once, so you will loose and loose badly. At least if you stand and fight you can shoot back. At any rate strong and weak are often local and/or temprary. If your 'weak' side doesn't stand up and fight, how are reinforcements ever going to make it to you? Or how can you save/prevent the enemy from doing whatever they want if you don't fight back? And how can you tell you are 'weak' anyway? with your observation planes counting the enemy? It's not as though battles have never been won by the side that was outnumbered, or that a strong stand by a numerically weaker unit in one part of a battlefield has saved an army, or allowed other units in other areas the ability to win the fight in the meantime.
One more thing, wouldn't it be better to lay down while reloading ?
you have to stand to load a musket. It wasn't until the advent of breech loading rifles in the 1850's - 1870's that it became technically possible to reload without standing up.