> This idea that "life support" is the most difficult aspect is unfounded.

It's an unknown. While we have manned rockets, we have never entirely isolated a group of humans from the biosphere for even a year, never mind indefinitely. The times it was tried, it failed. As the article points out, it is not an experiment that can be done piecemeal. All elements must be in place and interacting before the effects are known: lack of gravity, radiation shielding, recyclers, scrubbers, years of time, etc