I totally agree with you. It seems to me a very arbitrary process that when a particular disability is identified, chances are that this person is automatically excluded.
That does not take into account the fact that telling you that a person has a given disability tells you a lot less than many people think it does. It doesn't tell you the particular degree of that disability, nor the person's background, attributes, and how they deal with the realities of their particular disability, nor does it speak to the contributions that this person might make if they come to Canada. I think those are contributions our society wants and needs.