Why does mainstream science refuse to give any credence to possible ancient aliens/technologically advanced human theories?

You say:

"The evidence is fairly substantial, from ancient monolithic monuments that we today would be hard pressed to build, to ancient knowledge of astronomy and mathematics that are completely out of place if you consider the level of advancement we believe was available at the time."

Not true. There is NO evidence at all for those claims. We <<know>> that ancient civilizations were very sophisticated in building techniques and in mathematics and astronomy. Just because you and a few others don't believe that Greeks or Egyptians or Mayans could build their temples, pyramids, monuments and so on does not mean they were incapable of it. They had thousands of available workers and decades in which to complete them.

You also say:

"There are educated, well respected SCIENTIST that hold theories in many various forms ranging from ancient alien involvement to theories of lost advanced human civilizations."

Please provide links to places where those "respected" scientists have posted or discussed their theories. Without the sources that back up your statement, there is no reason for anyone here to give them any credence.

Mainstream science doesn't find any credence to possible ancient aliens/technologically advanced "human" theories.

Your so-called "human" theories or not even Science.

Why the heck you are hell-bent on convincing Scientists say that there is credible evidence in these (your) theories? What do you gain from it? Go ahead & do what you want, with your theories, please. Leave the Scientists alone.

Mainstream Science doesn't refuse to give credence, there simply in no good reason to give credence. You can't believe what you see on TV shows or read in books. Here's an article you can read for a different perspective.

http://www.csicop.org/si/show/help_im_being_follow...

If aliens crossed millions of miles of space just to help humans construct big pointy piles of rocks they'd have to be as daft as a brush.

Because it's silly nonsense devoid of any evidence?

History is not a science.

You'd need evidence to support either case, and there isn't any.

Because it's not science and those aren't theories.Simply put.

Because upon examination, all such ideas have turned out to be bullshit.

because, for many "scientists", their egos will not allow them to consider that any other life form could possibly be more intelligent than they are....