From what I've read, MTBE isn't as bad for you as what you'd make out.
The IARC, a cancer research agency of the World Health Organization, maintains MTBE is not classifiable as a human carcinogen. MTBE can be tasted in water at concentrations of 5 – 15 µg/l.
MTBE is not classified as a human carcinogen at low exposure levels by the International Agency for Research on Cancer (IARC). However, exposure to large doses of MTBE carries significant non-cancer-related health risks. The effects of the prolonged presence of this alcohol derivative are not fully understood.
As of 2007, researchers have limited data about the health effects of ingestion of MTBE. The United States Environmental Protection Agency (EPA) has concluded that available data are not adequate to quantify health risks of MTBE at low exposure levels in drinking water, but that the data support the conclusion that MTBE is a potential human carcinogen at high doses.
Only in high doses.
In much the same way the Methanol is quite dangerous (It's actually lethal) at high dosages.
10ml of Methanol = blindness... 125ml = Death... But as little as 30ml is known to kill.
MTBE is still used as a fuel additive, at the petrol pump today.