I think what Rebdoniel expressed is a legitimate opinion.
He didn’t address having no army, which I haven’t seen an argument for. He addressed keeping a specific group out.
I haven’t seen the argument that given current political circumstances, we don’t need an army. If the entire country were frum, and everyone was a masmid (and moshiach still hadn’t come, and the Arabs still had the desire for “v’lo yizacher shem Yisrael od”, of course some people who would otherwise be learning would need to be in the army.
But that’s far from the reality. There’s an army which presents a very reasonable hishtadlus, but there’s never such a thing as “enough” learning; not for the actual mitzvah, and not for the “magne umatzleh” which it brings about.