There are two major sources of manpower within the early modern state, the dregs of society as commonly seen in popular fiction or Voltaire but also they came from the cities that didn't give a lot of chance for work or the country, where men could be interested in some adventure or work. From here they would report to a recruiter, which would get a bounty for each head they'd get. From here you'd be sent to a regiment and usually serve six years in a regiment.

Naturally, line soldiers wouldn't be given much respect. They were machines of war, they marched in a line and didn't do anything else but serve (sometimes they'd be contracted out to builders to work for pay, which the regimental commander would get and give some to his troops). There is little honor, before the Revolution, the concept of serving your nation doesn't hold much traction, even in Prussia.

However, even though you're having "thousands" march to their death, no more than a couple of thousand would ever truly die in a battle.