It can be a little depressing being a Tokka fan. I felt like laughing at adversity to cheer myself up.
It seems to have helped.
For the record, incest is a valid excuse against Lin being Sokka’s biological daughter. But only if we stick to the definition: incest is the illegal act of having a sexual relation with someone who is too closely related to you. If it’s not forbidden by law, it’s not incest, no matter where else it’s illegal or how taboo it is.