He would likely be better off if they simply reported that the Democrats of the MA delegation did this, not mentioning him at all. Many might then think that Brown was simply not asked. Had they done that, it would likely have been a little article that received few comments. Instead this tries for a more controversial story.
From the comments, it looks like his excuse is not flying. I suspect the reason is that for people who thing the PSA is a good idea, including many independents and most young people, it sounds comply lame and possibly even untruthful or cowardly.
I don't know anything about Savage, but as you said it is not relevant. This is an effort so mainstream that, per some articles, the Red Sox, and the employees of VISA have recorded theirs - here is the collection of them -
http://www.itgetsbetter.org/video/What I suspect is that Brown is afraid (or agrees with) the social conservatives, who believe that homosexuality is a sin and a choice. They then see this as condoning what they think is wrong. Brown siding with them over the welfare of teens really is pretty sad.
Teen years are often hard, but dealing with being gay does make them harder even with supportive families in blue states. Having leaders, athletic heroes and stars making this effort really should help. It could make a gay teen feel more accepted.