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.
Military recruitment standards are pretty much written with middle class white kids in mind. The crimes that will disqualify you are predominantly done by the poor, the tattoos that will DQ you are predominantly associated with black people, the drug policy is straight out of the Nixon campaign playbook, etc. Of course, there's a waiver for all of these if you need to get one, but then that hides discrimination behind the recruiters themselves who will push harder to get kids that look like themselves over the line due to implicit biases.
Military recruitment does still lie to white kids though, and that can't be fully discounted. If you grow up in a culture that tells you from cradle to grave in every waking moment that joining the military is an unqualified good, and then you are looking at the capitalist workforce and see only soul crushing jobs that don't do any good for anybody, then it's very easy to see why joining the imperialist violence doers is such an attractive option for anyone that hasn't been radicalized against imperialism (which is like 95% of America including half of all self-described leftists).
I would say save your sympathy for people who not only regret what they did but who are doing some kind of working or organizing to make up for it, and also that agitating for the left among the military is a waste of time compared to doing it among the currently politically disengaged.