I appreciate you being forthcoming and if what you said was candid, then you definitely sound like a stand up guy. However, do honestly ask yourself this:

Is there proportionately more losers amongst the subset of white men who go to China to teach English than the subset of white men who don't?

To most Chinese, the answer to that question is obvious.

And sure, generalizing the behavior of these bad ones to the whole group may be extremely politically incorrect, but people notice deltas much more than absolute changes. So even if these degenerates still objectively make up a minority of the expat population in China, a proportional increase in their percentage relative to the normal white control population in the west will still be readily picked up upon by us Chinese Americans who understand both cultures and have lived in both China and the west. After noticing the existence of such a difference, then the human brain automatically starts to theorize on potential mechanism which could made this happen, hence the stereotyping and generalizations. This cognitive ability of ours to generalize via stereotypes was an excellent survival tool that has evolved over hundreds of millennia, without it we would not be nearly as successful as a species. So from that lens, I hope you can see why people like us go with our gut instincts on these matters.

And lastly, ethnocentrism and nationalism exist in ALL groups of people. At least I'm not being a hypocrite about it.