According to the Geneva Convention’s rules of acceptable warfare, combatants should be clearly identified, meaning that they cannot be permanently masked. Russian President Vladimir Putin has flouted these rules, first in Crimea and now in eastern Ukraine. The proof of Russian military involvement in Ukraine is convincing. The fact that Putin commands a nuclear arsenal is why the West is, understandably, reluctant to confront the Russian leader. But Putin must be stood up to, first with a diplomatic and economic assault and then, if he continues to invade peaceful neighbors, militarily confrontation.
EuroMaidan Revolution demonstrators also wore masks, which unfortunately had the effect of frightening the Russian population (at least according to Kremlin propaganda). However, they were not representing a government, but rather fighting against a corrupt and violent one. The demonstrators, as such, had more justification for hiding, but we still would have preferred that they identified themselves. But when it comes to state police and soldiers, there is no excuse for armed men wearing masks and helmets and hiding their identifies. It amounts to terrorism.