Religion is easily defined as a communicable form of mental illness. Some variants are more benign than others, though it is generally the more virulent that propagate most effectively. Weaponized viruses rule.
As far as the difference between atheism and agnosticism, think smurfs. Agnostics are polite enough to say that maybe there really are smurfs somewhere, while atheists come out and say that you must be joking.
The 'logic' by which people support Scientology or Islam or any other compendium of patent nonsense is rarely more than a study in applied fallacy.
As far as the warm fuzzy feeling that religion gives, the Onion has it nailed: https://www.theonion.com/war-torn-middle-east-seeks-solace-in-religion-1819568630
Coming to the idea of 'morality,' the moral standards of religion have been behind much of the most truly evil behavior in human history. The religious texts I have on hand mandate genocide, slavery and a host of other things that I personally find deplorable. YMMV.
If it is only the instructions of a mythical construct by which you would live you life in an honest and ethical manner, there is something wrong with you.
BSBd,
Winsor