Would they even know that he's Kyle the Hero?
Unless we're being meta, or poorly written, most hero/demon king stories are medieval-fantasy. The average solider is a commoner with little-to-no idea who, or even what, the hero looks or sounds like.
And generals, while typically being nobility, also would likely never have seen or heard the voice of the hero either.
So, ultimately, what I'm trying to say is: They're fodder and unless he takes his helmet off, they'll never know.
And besides, heroes fight against injustice. Obviously burning down neutral villages and enslaving Japanese Kobolds is an injustice.