Okay, so the Sci-Fi Channel didn't really catch syphilis, but it did catch an equally horrible disease: Marketing Myopia.
There are very few reasons to change a brand name, most of which revolve around having such a poor public opinion of your brand that customers will not trust you. In the case of Sci-Fi Channel, I don't believe their viewers were running away from the station.
No, the powers that be wanted a name that they could trademark. Sci-Fi is a generic term that refers to the genre, and therefore they cannot trademark "Sci-Fi." Also, their programming has always been more than just science fiction, so they wanted something that was not so limiting in perception. The first point, ownership, is a nonsense reason to pursue a name change. They had legal protection for the name "Sci-Fi Channel" and the related logo. Now, I can give them a little credit on the second point. It is important for customers to hear your name and instantly know what it stands for.
But here is the problem, their customers already knew what to expect from them. Brand equity existed with the old name, and ultimately it made sense. Not everyone on earth strictly defines science fiction the same way. There was no need to change the name to broaden their scope. Even if the argument was to attract new viewers, what is the sound they will hear? It still is pronounced the same, but now they have lost the inherint definition of what viewers can expect from the channel.
What has the name change accomplished? Likely made some design firm money to design the logo and change their collateral material, added confusion, and gave their loyal customers a reason to have a grudge against them.
Fiscal irresponsibility and angering customers. Hmm, isn't that the opposite of what marketers should be doing for their firm?
For a great counterpoint in support of the name change, read SUb's post on Why Syfy is a Good Idea.