I got the same types of people in Europe insisting they never turned away spirits. Usually I put on my best concerned face:
"Gosh, do you also tell your kids to always trust strangers? Do you tell em, 'Go with that nice man in the trenchcoat with prison tattoos!'"
-said like I'm talking down to a child.
The crowd generally started snickering and the questioner's face fell. That's when you really want to pour it on, since subtlety is often lost on some of the ones who've been misled or are lost in their own little world:
"Do you also eat any mushroom you find in the woods? You do know some of them are poisonous, d-o-n-t y-o-u? Some spirits are dangerous. Some spirits LIE and HARM people and take JOY in tricking others. The only place where you should always trust spirits is...FANTASYLAND!"
Mo, I also think the same answer works for both the Indian spirit guide and I-was-Indian-in-a-past-life:
Find out the tribe (Its always a famous tribe like Lakota, Comanche, etc, never one of the California or northwest coast tribes.)
Then say "Congratulations on speaking Lakota fluently! Let's hear you tell all about what your guide said/what your past life was like, in Lakota, no dictionary, no going to actual Lakotas to get a translation! Now!"
And for the racist ranters, usually theyre beyond hope. The main thing I would do is try to embarass them in front of the crowd so as to turn others away from their ideas. Something like:
"So do you tell Jews to just get over the Holocaust? Do you go to Harlem and lecture Blacks on 'The problem with you Blacks is...?'"
Usually plugging in another ethnic group so people can see just how racist/condescending/hostile the speaker is works pretty well.
And then again, you can try simple sarcasm. "Thank you for having the unquestionable solutions to fix all our problems oh Wise One. That is mighty white of you, oh Great White Father."