Not true. Many theists claim that the existence of God must be taken on faith alone, and that you can't
know whether or not God exists. These are agnostic theists.
(
ETA: I see you posted something to this effect while I was composing this response.)
Usually the excuse they give for God withholding evidence of his existence is that to prove he exists would take away your free choice to choose whether or not to believe in him.
True.
Agnosticism is a position about whether or not these claims of God are substantiated. Atheism is a position about whether or not these claims are true. These are positions on two different things, as Wollery pointed out.
So your assertion that agnosticism is "atheism in denial" is false.
That's how Thomas Huxley originally defined the term, and some people still use that definition today.
But lack of belief or disbelief in God is now known as "soft atheism" (or "weak atheism" or "negative atheism", depending on who you're talking to).
Actual disbelief in God is known as "hard atheism" (or "strong atheism" or "positive atheism", depending on who you're talking to).
Sadly, many dictionaries give very poor definitions for atheism.
Here's the definition
from Webster's: