Can I do volunteer work on a tourist visa in Thailand?

Okay, people volunteer all the time without any adverse effects BUT the real rule is whether it's paid or unpaid volunteering requires the proper visa and work permit.

I think the O/P can make an educated decision on what they want to do

Official by law, yes , the Non Immigrant O visa based on Volunteer and the Work Permit for Volunteer. Benefit is that you also get insurance in case of, as you know more and more areas in Thailand get the red zone rabies reports. But as on many things law enforcement is low. Don't believe the I hear stories, best example is I heard my good friend got arrested with a SWAT team fully armed, using explosives to blow out the door because he cooked his own breakfast and made a cup of coffee in his own house. He took away two jobs, one as cook and one as waitress by doing it all himself without a work permit and the appropriate Visa. He went to court and got sentenced to life in jail, than he woke up from this bad dream and prepared his breakfast without problems.

Be careful, thats illigal. You will get arrested working here without permit

Technically and stricktly by law you need a Work Permit. Even the volunteers after the Tsunami needed one.

I'm hoping Soi Dog collects strays and has them vaccinated, tested for rabies and has them spayed or neutered and not just feeds them so they can make more stray dogs.

Technically you need one but I wouldn't bother getting one if you're only around for a short time

Seems a bit counter intuitive. Volunteering to do something is not work when it is free. If you see trash on the road and want to pick it up you are volunteering to do so. Working involves making money. If no money is involved, what's the problem?

I remember some people getting in trouble volenteering in the clean up after the tsunami

You need a work permit even to do voluntary work.

Officially, you need a work permit to do this kind of work. But this is Thailand, for lack of better words, who knows. Some people actually pay to teach here and there are agencies that are built on a pay to volunteer model and officials turn a blind eye. I'll take a wild guess and say that if you pay anything to do this, then you're probably fine.

Volunteering requires a work permit, and you cannot get a work permit while on a tourist visa, you would need a non immigrant type O visa.

ANY work conducted in Thailand weather its a real job or volunteering requires a work permit. They have specific ones for volunteers

I think technically illegal. Will you have a problem, probably not. I'd assume immigration have better things to do with their time.