I can think of about a billion reasons not to build E. coli from scratch

*Reason #1: E coli bacteria live in our guts. Want a mutant one that makes botulism toxin that kills swiftly, with massive lethality? Hey, no problem!

http://www.newscientist.com/article/dn17514-evolution-machine-speeds-up-search-for-better-bugs.html

*Then again, this massive broadscale mutation technique looks plenty cheap and highly suitable for a favela bathtub, so what the heck, boys, have at it!