It's an incorrect frame for a few reasons and the two columns are more evidence that Tierney has as much business writing about science or its ethics as Newt Gingrich has running a charity for children.
First, as with most libertarian ideals, keeping the government out of personal situations sounds good on the surface. But what to do with parents who want to force a sexual orientation on their children? Some fundamentalist Christians already go to great lengths to remove 'teh gay' from their children. However, getting into that discussion is exactly the heated debate the Tierney wants at his blog, which brings me to the second reason that his frame is off.
John writes as is if, or at least his tone assumes that, the drugs for switching humans to a bisexual orientation currently exist. They don't. He seems to badly want to stir a controversial pot. Beyond attracting reader to his blog, why do this?
Third, the behavior expressed by the fruit flies was bisexual, not homosexual. Both the Nature Neuroscience abstract and the university press release that John link use 'bisexual' and 'homosexual' interchangeably, but describe bisexual behavior. I'm not sure why the researchers chose to do that, but John either needs some help with prefixes, or is being misleading. He very well knows there is a difference between the two in everyday discussions of sexuality. He probably figured the title 'Turning Bisexuality On and Off' wasn't as sexy (read traffic generating) as 'Turning Homosexuality On and Off.'
The bottom line is this: avoid traffic-hungry Tierney for all things science. Instead, check out Nature's top five science blogs. There are some interesting, and controversial should you need that, sources of information there.