Why be a vegetarian?

I suppose there are two main reasons people become vegetarians. One
is for overall health. Plenty of reports are available singing the praises
of an all vegetable diet, and the ill-effects of meat, especially red meat.
The other big reason has to do with the ethics of raising animals to
kill them. Especially considering the conditions nowadays of "factory
farms" and the mass production of animals bred only to gain more
and faster profit.
However, noble and true as both of these arguments are (and perfectly
good reasons enough), neither is actually what started me off on this path.
More on that another day.