I feel like censoring it would be unethical, while refusing to host it would simply be poor form.

Livecasting of own suicide: freedom of expression + freedom to make choices with regard to own life.

Edit: This is not to imply that Tumblr is not entitled to do whatever they damn please with their own website. But, should someone build a website specifically for livecasting suicides I would very much disagree with its censorship.