This movie is very similar in subject matter, theme, structure and tone to the Danish resistance historical film, 'Flame and Citron', staring Mads Mickelson and Thure Lindhardt. That movie also asks the question, 'Was it worth it?'
The answer in both instances--in all instances where brave people struggle against tyranny--is always of course yes. I'm frankly surprised filmmakers think it is somehow a complex moral dilemma. Of course innocent people died in reprisals after Reinhard Heydrich was assassinated. Many millions more died at his hands while he was alive. Heydrich was the architect of the Holocaust. Heydrich was the leader of the Einsatzgruppen which executed over a million people by rounding them up by the thousands and shooting them into ditches. Heydrich was the founder of the Gestapo. Heydrich murdered and terrorized and oppressed wherever he went. He was also by far the most capable and intelligent of all of the high-ranking Nazi leaders. Killing the most brilliant and dangerous of your enemy's leaders is a vital objective in any war. Imperial Japanese Admiral Isoroku Yamamoto's flight was intercepted and shot down in 1943 for exactly that reason. So yes, Heydrich's assassination was necessary.
'Anthropoid' is historically correct on all of the major plot points, with some artistic license taken for dialogue and characterization. History buffs won't be disappointed. Neither will those who just want to watch a good--and sometimes great--movie.