We can debate whether each of these is good or bad. But marriage has been under assault for years. We can't say no fault quickie divorces are acceptable but gay marriage isn't. It all weakens marriage.
They may not have been large in number, but they were extremely important to the flow of history.
Many of these marriages were blessed, performed, and/or attended by the highest religious figures of the time.
The participants may have loved each other, yet we are told that in some cases the husband and wife often hadn't even met before they were wed and didn't see much of each other after. There may have been children, but again this was more for continuing the legacy rather than to go forth and multiply.
Marriage has been used, misused, and abused for centuries.
I'm not stating this as an argument in favor of gay "marriage", only saying that these are facts that must be confronted in any defense of traditional marriage.