It is extremely misleading to compare the binding affinity of a partial mu opioid agonist with profoundly different molecular structure to the binding affinity of a full mu opioid agonist. Mitragynine is not 13x more potent than morphine in any effect observed in vivo. Preliminary research shows that the novel binding mechanism of mitragynine results in drastically different effects (supposedly by selective avoidance of beta arrestin activation). For instance, it does not cause respiratory depression to a significant extent in mammals.
Thyroid dysfunction and liver damage have never been demonstrated in a study, and anecdotal reports do not seem to suggest that they occur.
The deaths in Sweden were attributed to an isolated metabolite of tramadol that is sold as a research chemical and was mixed into powdered kratom leaf. There is no evidence that kratom contributed to those deaths.
I encourage you to read the "Talk" section of the Wikipedia page before repeating claims in the article without context.
The effects of kratom are extremely mild, you vomit quickly if you take too much, the withdrawal symptoms are comparable to caffeine, and there has never been a death attributed to kratom alone.