How is that different than an officer's wife? They get paid less don't have a nice quarters, have to salute you. You repay that loyalty by screwing one of their wives.
At least officers are within the same broad peer group. But as officers, we are given a host of privileges, and great authority over enlisted. It's why the most junior troops eat first, most senior officers eat last. Our greater privilege come with a greater responsibility for their welfare. We owe them that.
Adulterous relationships on the military are always bad, for many reasons. But when it is the most powerful taking advantage of the most junior, it is particularly heinous.