When the faction was originally split into four families, the Xue family was given the Frost Sutra. The primary reason for this was how well it suited them.
The Frost Sutra relied on yin power and the ice element. Members of the Xue family had a body-type that was comprised of both traits, which made them the best candidates to learn it.
That being said, the Xue family always knew there'd be a problem if they were to learn it. Before the sanctuaries were discovered, humans were weak. And for the Xue family, that meant they could only learn a portion of the Frost Sutra.
Rarely was someone's emotions affected by its learning back then.
And furthermore, Iceheart was designed to erase the negative emotions that arose from its learning.
But through the sanctuaries, as it was for every other family, they became stronger. And as a result, the effectiveness of the Frost Sutra increased.