I have read Imanuel Kant… As much as I can stand of it, anyway.
The most obvious argument against his work that I can think of, runs along these lines…
If the mind of man is invalid, as he repeatedly suggests, why should anyone take Kant (whom, I perhaps incorrectly believe, was a man at some point in his life) seriously?
I have yet to meet anyone who has successfully argued their way past that glorious contradiction.