User blog comment:Supahbadmarine/Official Canon Policy/@comment-77.78.234.37-20130227181608/@comment-2253300-20130228174917

They wouldn't even get that far. The Chapter would have been purged long before it came in contact with the Tau for having Xenos sympathies. On that note the idea of the flaw, and don't take this as an insult, is a little ridiculous. Most humans have never met a Xenos outside of hostility in this setting. A genetic flaw that makes you love aliens? Does that make sense to you? Besides as stated however strong the nurture side of this flaw is, the nature side of their indoctrination would cancel it out. If the flaw was strong enough to ove3rcome that then the Adeptus Mechanicus and Inquisition would notice early on.