People have no problem eating or drinking what I make.
Like I said before, if it does not taste or smell clean, like what you would buy from a store, then you are doing something wrong.
If your yogurt or kefir has anything other than the lactic acid tang, and in kefir some carbonation, then it is likely contamniated with other types of bacteria.
For example Propionibacteria will give it that dirty socks smell like Limburger cheese has.
However not all the bacteria and molds that produce off flavours are as friendly as the ones that give us stinky cheese delicassies.
Read this:
Update: Stonyfield Recalls YoBaby Yogurt Cups for Potential Coliform Contamination | Food Safety News
Other contaminants can be far worse.
So if your yogurt or kefir is smelling like roadkill throw it out, wash and sterilize everything with bleach or boiling, including counter tops, before starting over again.