Clearly, putting actors through war just so they'll be able to portray soldiers in battle believably is nothing a sane person would consider. But that doesn't mean that doing what 1917 does is a good idea: having soy boys portray men of arms. The performance of the main actors makes it just too painfully obvious that, growing up, they were never yelled at, slapped, punched and never had to endure any other significant amount of physical discomfort, i.e. never went hungry, never froze and, presumably, never had to walk more than a few bus stops. Being unable to fathom/understand even low-level intensity of violence and suffering, they seem bizarrely out of place in a WWI-setting. And that, in turn, makes for something worse than just a boring and non-immersive movie: a mockery of the unimaginable pain and sacrifice their grandfathers went through in order to keep Europe free.