Would gay marriage qualify legally for getting immigration papers?

No.

As others have said, the marriage only gets you the right to apply for a visa.

But beyond that, that is a federal marriage right. Same sex marriage is not recognized on any level by the federal gov. Several states have same sex marriage, but the federal gov does not recognnize them, nor do other states.

Finally, in response to the answer above mine, no, legal same sex marriage does NOT offer the same rights in the US. Even on the state level, there is not a single state that offers same sex couples the same rights as they offer opposite sex couples.

Yes, although being married doesn't 'get' anyone 'papers'. It does allow one to apply for a spousal visa, but that visa still has a number of conditions and is not automatic. For example, a spousal visa requires that the applicant either have an existing legal visa OR be applying from outside the US.

If gay marriage is legal, it implies all the benefits of any other marriage.

Heterosexual marriages don't qualify legally for getting immigration papers. The spouse still has to meet certain qualifications.