There's no reason for you or me to be supportive of Microsoft in this situation.
Indeed, it's a fiduciary obligation to the shareholders given they are a listed company.
Second, it's not only that guy who's at loss, it's also all the people who used or might use his software. Are those people responsible for Russian government's actions too?
Why shouldn't people who collectively, i.e. en masse, support their government by actively disrespecting other country sovereignty and border (e.g. visiting Crimea) shouldn't be hold responsible? I think they should! And it looks like I'm not alone, check out the list of countries who support sanctions against Russian companies and individuals. As for the damage done to the OSS, I believe it's pretty minimal. He'll just move his stuff to GitLab, end of story.