How could possibly someone think humans used to be monkeys?

Because some idiot who doesn't even slightly understand evolution told them that that's what liberals think, so when they became liberal they decided to believe it.

its even sadder than that. we came from DNA goop.

Why did Americans not evolve a brain? You really need to read On the Origin of species by Charles Darwin. You sound stupid uneducated and an American. Evolution has been observed,

The only people believing that particular lie are Christian idiots who have no idea what evolution is and what it is not......

Some of us have enough brain cells rubbing together to be able to understand the concept of interpreting evidence to deduce fact that exist in the range BEYOND the bleeding obvious.

they dont think , monkeys have a different amount of chromosones than we do , and are incompatable , sorry for the bad news .thats why a sparrow doesnt breed with an elephant .

Nobody with half a brain would say, "Humans used to be monkeys."  However, it is true that a line of apes that eventually gave rise to humans descended from a monkey ancestor that lived about 35 million years ago.  And some humans, at least, are turning into something else with time.  Some humans are turning into uneducated non-thinkers who are too lazy to study basic information about what science has discovered over the past 160 years.

Strictly speaking the proposition is that humans and monkeys once shared a common ancestor that was something like a modern monkey or lemur. It is proposed that the last common ancestor we shared with another genus was with chimpanzees about 7 million years ago.

Of course this is total nonsense and is not supported by scientific evidence. [edit]DNA alone is enough to disprove it.

Actually, humans used to be bacteria for the majority of our time spent on Earth. But I seriously doubt that your mind is capable of grasping such a reality. No offense intended. 

We didn't used to be monkeys.

We do have monkey ancestors.

We also have bony fish ancestors.  We aren't fish.  We didn't used to be fish.