Starfleet Jedi

I've become quite the WH40K fan of late, devouring numreous books and reading up on the universe but one piece of info I can't seem to find out:

Why does the Imperium blind it's Astropaths?

I read Blind but it didn't contain any answers that I recall but I may have not been paying enough attention.

Wikipedia says it's a side effect of being spiritually joined to the Emperor to enhance their powers. Not sure what the source for that is, though.

It might force them to rely on their powers by removing their ability to see physically, so they're more powerful.

I got an answer. From another forum I post at.