I know we've been around this block many times, but it's useful to separate out the definitions of "marriage" and "civil union", as is done in many other countries.

A "civil union" has legal consequences concerning taxes, parenting, inheritance, power of attorney, and a variety of other issues. (Hint: dual income gay couple pay *lower* taxes because they must file separately. If they filed jointly, they'd inevitably pay at the higher rate for their joint income.)

A "marriage" is a spiritual thing, typically sanctioned by a church or other religious organization, the details of which vary but generally include aspects like life-long commitments to one's partner.

What "gay activists" want are civil unions, because they want the legal protections and are willing to take on the legal obligations. They wouldn't mind also being "married", i.e., considered full-fledged members of society. What concerns "right-wing activists" is that granting such rights to homosexuals will cause the collapse of our society (e.g., humping of box turtles). To the extent that we have any objective evidence of the effects of gay marriage on the rest of society, they appear to be negligible or even beneficial (citation: Massachusetts, despite allowing gay marriage, has the lowest divorce rate in the 50 states). Correlation does not imply causation, but the lack of correlation does serve as a counter-example to causation.

The deeper concern, so far as I can intuit, is that "gay marriage" is considered to be an abomination by a segment of the population, and any state recognition of gay rights (marriage, civil union, or whatever else) would undermine religious or cultural biases against it. State sanctioned marriage would clearly lead to more gay marriages (particularly starting from zero such marriages today). The "it's an abomination" crowd might conclude that state sanctioning caused the rise in gay marriage, perhaps by contradicting their religious / cultural message that opposes it. The "gay" response would naturally be that they've been gay all along, thank you, leading to the "nature" vs. "nurture" debate. If you believe homosexuality is a learned (and undesirable) behavior (i.e., comparable to drug use, criminal behavior, etc.), then you can legitimately argue that mainstream culture could / should take steps to avoid legitimizing homosexual culture. If you believe, however, that homosexuality is an inherent behavior, then culture has nothing to do with it, and you would by extension believe that the gay population, as a distinct group, deserves civil equality in precisely the fashion way that women and minorities have fought for in the past.

As such, there will always be an impasse between "gay rights" and "family values" because they have fundamentally opposite beliefs about the causes and social acceptability of homosexuality. No amount of debate or even scientific evidence will ever address these different worldviews. In short, we're doomed to have this argument over and over.