I believe by "homeland defensive postures" the commenter you are replying to was suggesting that, because our infrastructure (electrical, hydro, fuel) is largely controlled by internet-connected security holes, the repercussions of involving ourself abroad would be to face consequences at home - something we are politically and otherwise unprepared for. In other words, our lack of a 'defensive posture' on infrastructure (i.e., a lack of hardening against cyberattack) leads to our lack of countering actions by China or Russia abroad.