You are wrong that it isn't hurting anyone. Spam takes up
bandwidth, disk space and time - without the sending paying
for it. If you believe it isn't hurting anyone, you don't
know the mechanics involved. And spamming might not be illegal
everywhere, but that's irrelevant. Ethical is not the same as
to stay within the margins of the law.
I wouldn't quit my job because of the colour of the bathroom
walls, but I have quit my previous job (and taken a 25% cut in pay)
because I strongly disagreed with the way management was acting.
I'd quit if my boss decided to go into the spamming business;
or if the company I worked for started dealing in weapons.
I've my views on what's good and what's right.
Do a google search on "Abigail's Oath".