I know it's too much to expect people to RTFA, but as others have pointed out it would take much more than 1 mutation. The main point the "doom and gloomers" are missing is that these modifications are designed to complement existing containment techniques.
Think of it as a potential way for researchers to more safely work with deadly bacterium such as anthrax. They would still use all of the traditional containment methods, but have an additional fail-safe built in. Ultimately these researchers hope to come up with multiple overlapping safeguards to provide even better safety.
It's beyond me, how anyone could object to making it harder for bacteria to escape from the lab!!