I've been riding motorbikes (from 125cc to 650cc) in Thailand since 2005/2006 and I promise you I have no death wish. Before that I rode motorbikes from north of the arctic circle to Paris in the south without accident.
In order to survive on a motorbike anywhere in the world you've got to have this attitude:
Everybody else in traffic are blind, they are deaf, they are probably drunk and they are all out to kill you!
Of course renting a motorbike anywhere (not only Thailand) without experience, without a license and riding without a helmet is very stupid.
But your statement that anyone who gets on a motorbike in Thailand has a death wish is pure ignorance. (I'm being polite)