"The politics of division"

Why is it that those standing up for traditional values
are described as practicing (“the politics of division”,
while those promoting non-traditional, radical, social policies,
such as same-sex marriage are not?

Arnold Schwarzenegger writes:

Now I’d like to speak to some of my fellow Republicans.
I know plenty of Republicans who are sensible and driven to solve problems for America.
They believe in Reagan’s vision of a big tent where everyone is welcome.
This message isn’t for them.

It is for Republicans who choose the politics of division
[my emphasis]
over policies that improve the lives of all of us.
[This is a false choice.]
It is for Republicans who have decided to neglect
the next generation of voters.
[What Schwarzenegger is referring to
is how shamefully our educational system
has failed to uphold the transmission of traditional values.
Making things even worse,
those determining the cultural milieu have all too often
worked to undermine them.]
It is for Republicans who are fighting for laws
that fly in the face of equality and freedom.

If we want our party to grow and last,
we must be focused on real solutions to problems Americans are facing.

We could start with infrastructure.
Traffic costs our drivers over $100 billion annually.
Airport delays cost another $22 billion.
Or we could get to work on education.
If graduation rates don’t increase, we will have a shortage of 5 million workers by 2020 —
not because we lack the manpower, but because the jobs will require education that our students aren’t receiving.
We could clean up our air: MIT researchers found that pollution kills more than 200,000 Americans every year — more than traffic accidents, homicides, suicides and our wars in Iraq and Afghanistan combined.
There are so many real problems that need solving.
[Fine, go to work on those, if they can be solved.
But retaining the traditional definition of marriage
hardly is a roadblock to working on those issues.]