Traditionally that meant armed forces, their bases, their supplies and so on. But the line has gotten awful blurry. Tech companies have become entwined with the state and are fundamnetal parts of both domestic and foreign policy. Targeting of military strikes is an obvious example [1][2].
I believe that in the very least these companies have risen to the level of defense contractors so Palantir is at least as valid of a target as Lockheed Martin, Northrop Grumman or Boeing. Is that sufficiently valid? I don't know.
But I don't think you can plead ignorance about what your tech platform is being used for, particularly if you're Palantir. You are helping a military force kill people and are deciding which people. You can't wash your hands of that.
[1]: https://www.972mag.com/lavender-ai-israeli-army-gaza/
[2]: https://www.business-humanrights.org/es/%C3%BAltimas-noticia...