Do you feel that as a result of their anger over the Red Wedding large parts of the fandom just give LSH a total moral blank check? She murders a mentally disabled man and an envoy under a flag of truce. Also, she is willing to execute Brienne, the one true knight in Westeros, Hyle Hunt, who at least fought the bloody mummers with honor, and Podrick Payne, a clearly non malicious teenager.

I think the mistake you’re making here is treating LSH like a normal human character. LSH is a manifestation of nemesis, and thus is a primal force of retribution, above ordinary considerations of morality. 

Did Merytt or Petyr Frey deserve to die? No. Neither did the children of Niobe, Chrysippus son of Pelops, the sons of Thyestes, Iphigenia at Aulis, or Cassandra at Mycenae, but the curse of the House of Atreus brought them to their deaths all the same. The curse of the House of Walder has yet to complete its business, but that’s what LSH is for.