This shows your age. Live a little, work a little and then you'll see the joke. It happens all the time. People who have zero knowledge/experience in charge of people who actually know what they're doing.
They weren't cautious because up to that point, they never had to be. They never encountered anything remotely similar to the Aliens.
Nope. Some bomb squads use robots to check out/detonate explosives but no police force/military force on this planet routinely use robots like you're describing.
That has nothing to do with "marines". It has to do with human arrogance. There's astrophysicists who believe life requires water in order to exist. Why? Because WE required water to exist. Which is why the search for life on other planets start with planets that have liquid water. Even though it's possible that life might not even require that. Hell, there might be some planets where life thrives in molten lava. Who knows!? But that's human arrogance for ya.
The same place she emerges from.
How much does an Alien queen weigh?
The reason why all the flaws in Prometheus are being discussed is because..
1. This is a.. you know.. Prometheus Discussion thread and..
2. Some people actually think this movie is flawless or damn near flawless. So that stance invites criticism.