Sombre Reflections: How much is a Human life Worth?

One thing I absolutely hate is people fabricating things to reinforce their extreme position. Can I give you an example:

MrMary: yeah So i really like that Elton John song RocketMan
Dude I know: You must be really gay like the duck wearing costume kinda gay

MrMary: yeah I think Education should be free
Dude: You’re like this extreme liberal

Today I saw an image on Facebook that gave me pause for reflection. It was on 9/11. I lived through 9/11 and it was a sad day. But here is the image;

I made the mistake of  vocalizing some of my thoughts which won me the ire of a few knuckleheads on my FaceBook.  But this is what I asked:

 How much is a human life worth ?

Are some human lives worth more than others ?

What is the limit to retaliation ?

Does retaliation by killing create the very conditions we sought to address ?

For every American killed 9000 people were killed, is this sorta ok?