Why can't we all just get along without prejudices?

Last week I was out grocery shopping at the local Safeway. As I was walking out, I noticed a young (probably in her late 20s, early 30s) Vietnamese woman, carrying a young (2 to 3 year old) child in one arm and negotiating a (rather full) grocery cart with the other hand. Now, this grocery cart was equipped with a "locking wheel" - which prevents the user to take the cart outside a certain boundary. (The mechanism used by these carts is explained here). So, this hapless lady was trying to take the cart to her car and the cart would not budge! (I learned later that she had given her car for an Oil Change at the nearby Service Station - which is the reason why she had to push the cart so far).

My immediate reaction was to explain to her that the cart has a locking wheel and help her with moving her groceries. Just as I was doing this, I heard a loud voice bellowing, "This is the reason they have locks on these carts. To prevent trash like you from moving the carts outside the store premises". I turned around and saw this short, portly, elderly, caucasian gentleman with grey hair, a grey stubble and glasses. His face was flush with anger and his eyes were almost popping out of his glasses. I suspect that the lady did not even comprehend what he was saying. She seemed quite flustered and was desperately trying to empty her cart and move the grocery bags inside to the sidewalk. I walked up to the gentleman and told him, "Come on, back off. She did not know that the cart wheels have locks." He then turned his anger towards me saying, "Why should I back off. I live in this neighborhood and regularly find these carts inside my complex. These people should go back to their country and trash it anyway they want." I determined that I could not "reason" with his. So I just said, "I don't think you are being fair. She genuinely did not know. So just back off, OK." I then turned towards the lady, helped her empty the cart and then moved the locked cart back to the grocery store. The lady picked up the bags that I had helped her move to the sidewalk and quickly walked towards her car after mumbling her thanks to me.

Luckily, everything ended well in this situation. However, I could not help thinking later about the choice of words used by the gentleman and his initial reaction. It rankled me that his first reaction was to refer to her as "trash like you". Should I have given him the "If you prick us, do we not bleed" speech (from Shakespeare's Merchant of Venice)? Are people truly walking around with such prejudices? Whatever happened to the "melting pot" and living in a "cosmopolitan" society. If this the case in California, what would be the "plight" of the immigrant population in the Southern Bible Belt states?

Am I reading too much into this (possibly isolated) incident? Share your thoughts as comments to this post.