The government is very powerful, and they're cracking down on mixers, so Theymos' decision to eliminate that risk was the right move. Otherwise, if something happens, the forum could get caught in the middle, and a lot of people would be affected. Basically, according to the government, mixers are used for money laundering, and there are even reports that terrorists use them to finance destructive weapons. Naturally, this puts them on the government's radar, making it easy for them to seize the mixers, confiscate the Bitcoin (which becomes government income), and throw the people behind the mixers in jail.