You forgot to add... "in my opinion" to the end of that statement.
He does have a point. Tieflings look different. They look scary, and people would likely be scared of them. Tieflings would likely be shunned, cast out of society, and such.
This happens all the time in the real world, with pretty much the same sentiment: "Blacks don't belong in civilized society." "Can't trust a one of those Muslims, I tell you."
Generally, though, time will bring about the necessary changes in perception to bridge the divide. Kids who grow up seeing that people who look different really aren't that different will remember that later on, and they'll pass it to their children, and so on.
So, tieflings likely wouldn't be welcome in small communities. But, in larger, metropolitan communities like larger cities, and after a few generations, tieflings would likely be viewed as really no different than anyone else. Some may have a propensity for evil, sure. But so do humans, elves, dwarves and anyone else.
That amount of time hasn't passed in the Forgotten Realms. It could have passed in your world, though. Tieflings may just be viewed as normal folk who had the misfortune of being related to some truly vile people. Or it could be that the sins of the father do carry to the son, even over hundreds of generations.
In my world, I have both types of places. But then, my isolated communities tend to hate anyone that's not like them. Small villages of humans dislike the elves that live in the nearby forest. Dwarves that don't interact with others races mistrust anyone that isn't also a dwarf, and so on.
it's all in how you want your world to be. Variant's view is quite valid for his world, and (not to single you out, but I've seen it too often on forums lately) I should add that "in my opinion" should be an understood part of anyone's post, unless said statement is accompanied by hard, verifiable evidence.