Why didn't anyone ever think of assassinating Hitler right off the bat to prevent 40,000,000 deaths?

It was more important to crush Nazism/Germany than it was to remove its leader.

Nazism is an ideology. Leaders can be replaced.

answer to the first question: people never thought Hitler would be that insane. they thought he was a great leader who rebuilt Germany from the ground up and payed off the debt Germany still owed from the first world war. Winston Churchill even said that if Britain ever got ruined they needed a leader like Hitler to rebuild them. Nobody knew he was a psychotic murderer

Oh you have much to learn my friend. There were only about 50 attempts to assassinate hitler, all which have failed. He was a tough man to get to, and even if you do get up close to him, you aren't just going to stab or shoot him when everyone is around. It was nearly impossible to kill him and get away with it.

Up until he became really aggressive with his military, many American companies supported him. Ford and GM built nearly all of the Third Reich's military non-combat vehicles, converting their plants to work only for Germany.

In answer to your second question - anyone even suspected of involvement was interrogated and executed and hitler became even more paranoid and cautious making a 2nd attempt even less likely to succeed.

1. they did try but the Third Reich was able to prevent them, or they just failed altogether.

2. They were fearful of being killed, but also were afraid of being successful and having high ranking Nazi's hurt their family and friends after they were imprisoned or killed

there were several attempts. Check out the link below

side note- the movie valkryie is really good. (and very sad)

If you actually go back and read history, there were a BUNCH of people who tried to kill them from the German Resistance.

http://en.wikipedia.org/wiki/German_Resistance

Wikipedia is your best friend.