John Kerry and Dick Cheney

I have been told it was one of John Kerry's greatest gaffes during the presidential campaign of 2004. During a debate with President Bush, Senator Kerry criticized Bush's stance on same-sex marriage. While doing so, he brought up Dick Cheney's openly gay daughter. Republicans everywhere were outraged that Kerry would drag family members into the media spotlight just to score political points.

Normally, I would agree. I find it disgusting the way the media has treated the Palin family and aired and amplified every minor sin of the Bush daughters simply for having the bad luck of being related to someone famous. However in this case, I fail to see what the big deal was.
The Bush daughters were not trying to make a political statement when they tried to purchase beer while underage. All indications are that they were hoping not to be recognized. On the other hand, to openly take on the identity of being a lesbian is to make a political statement. Cheney's daughter's sexual orientation was not only commonly known, but the Cheneys themselves had brought up the subject in the past. Nobody was trying to hide the facts or seemed hurt that they had escaped. It was not as if Kerry released secret documents that until the debate had never been known to the public. It was not as if Kerry was insulting Cheney's daughter - far from it. What Kerry did was merely a common debate tactic to imply some sort of hypocrisy on Bush's part. A stretch, to be sure - but not unusual. He probably didn't even plan it. One has to understand the mindset of those that push for same-sex marriage. They see rejection of their opinion that they have a right to marriage as rejection of their very value as human beings. That one could choose as a running mate one who still accepts his daughter as a human being while simultaneously rejecting her fundamental human rights, seems to many in John Kerry's base as hypocrisy.
As I am used to hearing this type of argument used all the time, I simply dismissed it as nonsense and moved on. I tried to understand the Republican outrage, but so far have got nowhere. Meanwhile, Democrats seemed to have no problem with it and made many of the same arguments I have made here. Am I missing something? Republicans, help me to understand your feelings, and maybe the Democrats will understand too.