What does this have to do with the half-exiles? Are many of them former nomads? The quote you're responding to is responding to their treatment as impure, getting beaten for trying to bake bread in the communal oven, things like that.
No, that was just my utter fail at reading comprehension. The Half-Exiles and nomads have nothing to do with each other.
The underlying reason that Half-Exiles are hated so much is most proximally because of Purity, but the issue also has roots in Joyous Symphony and Greater Justice. Half-Exiles are ultimately criminals sentenced to penal labour. Historically, that is not a popular group and Ymaryn culture is not particularly kind to those that break social norms. This type of hatred and violence directed at historically unpopular outgroups is pretty common. The Cagots occupied a similar place in pre-modern France; they're no religiously or ethnically different from their neighbours, but rumours of spiritual impurity dogs them across generations, leading to immense social ostracism. The difference between Cagots and Half-Exiles is that the latter do not face the legal discrimination that was used against the Cagots.