Just for curiosity, why do you think that whoever wears a "Kefia" (or however you call it) and holds a weapon is a terrorist? Is there a reason, or is just the result of a strong "propaganda" you have been submitted to?
Couldn't the man on the left just be a civil fighter? ...or perhaps in your countries you never had civil fighters and you have always had only soldiers?

Concerning why they cover their face, I guess it is because they don't want to be identified, otherwise themselves and their families would be in danger also during daily life. Of course this is not a problem for a marines, who can show his face because he never fights IN his country, but always outside, and his family is fae at home.
Partizans during WW2 used to cover their faces for similar reasons, and they were not terrorist, but great fighter that opponed the German Army, and they surely were not cowards because their life was VERY risky.

I think you should reflect on the difference between fighters and terrorists thinking of how differently they behave. Have you ever had terrorism in your country? If you are from USA you should, sadly, know that when terrorists attack they don't hide their faces, they hide the fact that they are terrorists, their mission is to kill innocent people or to destroy something and they don't reach their target with covered faces, otherwise anyone would understand that they are terrorists and they could be stopped before accomplishing their mission.