The main issue is that too many people (sorry, most appear to be conservatives) feel that the term marriage must be consistent in both a legal, governmental context along with a social or religious meaning.
I see no problem with two people of legal age being married in the legal sense which effectively provides inheritence rights, health care benefits, certain tax advantages, etc.
The moral or religious view of marriage is TOTALLY a different issue.
For example, when the Catholic Church does not recognize a marriage due to a prior divorce, should that change the LEGAL status of the marriage ? Absolutely not.
Conversely, when a religion allows polygamy and accepts it as a "moral" practice, is the govenment conpelled to view it as such in a LEGAL manner? Absolutely not.
Mixing the religious view of "marriage" and the governmental view of "marriage" is practiced in many Islamic countries. Is that really what some people here want ???
***** Rub a Dub