There is no number of foreigners that is unacceptable to sacrifice for a middle class livelihood. Anti-cop because they can imagine a scenario where a cop inconveniences them. These principles don't apply to the Waffen SS because they can't imagine a soldier personally inconveniencing them and, of course, foreigners aren't really humans.
The comment's been removed, so you may not be aware, but they were the one who made the stakes "kill or be killed." I'm pretty sure I was even quoting them there.
If their argument is that it's ok for Americans to join the military and kill people abroad because otherwise they'll die, then that's the framework I'm going to respond to.
You can respond to it, by saying that it is in fact bullshit, and leaving it at that.