Well, it could be worse you could go to an uncivilized country like the USA and drink Grape or Apple juice and get 10% arsenic. E-coli is also a danger in the US. Frankly, food safety here is no picnic. I assure you, if you knew what you were eating and drinking here in the USA, you would have just as serious reservations about doing either. You are going to a different country-not a different planet. I would have greater reservations perhaps in China but you may have noticed there are over a billion chinese. So they obvioiusly aren't dying like flies because of poor health conditions.
It is true that street food in Thailand may have bacteria but for most people it really is no different than eating here. You can not avoid all of life's dangers. There is "playing it safe" and there is "being paranoid". Unless you are highly prone to food poisioning I would not worry about it. As for water, every hotel I have ever been in there says whether or not it is potable. I have eaten street food in Thailand, Cambodia, Vietnam and the Philippines and i never had food poisioning or an upset stomach. The original poster said it right. Just do what you would do here-look and see if the vendor appears clean and neat and he handles the food appropriately. In NYC they have a rating system for cleanliness and I assure you some places come up with "unhealthy" ratings. I wouldn't eat at one of them either.
I think when Americans go to these countries and act like they should wear face masks and latex gloves everwhere they go, they are sending a very condesending message to their host country. You probably had a better chance of getting sick or injured drivng to the airport than you did getting sick in the foreign country. And I assure you that you have a better chance of getting sick in a US hospital than you do getting sick by eating street food. Over 100,000 people each year get sick in US hospitals (many of them fatally). Strangely, I don't see a big outcry to avoid cars or hospitals.