Descended as I am from a Swiss mercenary who was serving in the French army, with his son, while his brother was in the (enemy) British army, I find the reasoning of many contributors to this thread downright odd. In pre-modern Europe, mercenaries (like my ancestors) were the surplus young men of poor countries with little agricultural land, often rented out by their own community leaders or clan elders. The practice persists to this day in the British army with the Gurkhas, and you don't have to examine the pattern of 19th- and 20th-century Scottish and Irish recruitment into the British army too closely to see a strong resemblance to the traditional mercenary pattern.

Today's mercenaries are also surplus young men with skills and experience they can't market anywhere else for such good money, so they take it while they can get it. They're still soldiering, but without the pension plan and disability insurance typical of first-world armies in modern times.