Military planes - Super Hornet, for example - have been using touch screens (UFC, in this case, the thing just below HUD) for over two decades now, and they seem fine with it, and newer ones use it even more. They don't seem to cause any problems.
Granted, stuff that's absolutely critical - like gear or the arm switch - is still mechanical, but UFC is still pretty mission critical, controlling eg IFF, autopilot, or radios.
F-35 has a 20" wide by 8" tall touchscreen. However, just about everything that you do on the touchscreen can also be done with various switches and selectors on the stick and throttle. There's even an equivalent of a mouse that will let you move a cursor around the screen and select items.
About the only things you cannot do on the touch screen are giving stick/throttle inputs and MASTER ARM on/off.
Granted, stuff that's absolutely critical - like gear or the arm switch - is still mechanical, but UFC is still pretty mission critical, controlling eg IFF, autopilot, or radios.