Posting after myself with more information...

Here's a letter from the WDMA regarding concerns about this bill backfiring...

We feel that the risk of backfire is very small. That could require that the initiative gets onto the ballot, is passed by the voters and is not struck down as unconstitutional by the Supreme Court. Such a chain of events is extremely unlikely.

If I-957 gets passed, it will almost certainly be rejected by the courts. That would require that the courts reject the premise that marriage exists for the purpose of procreation and either invalidate the laws based on that premise or force the Legislature to change those
laws.

Assuming we get enough signatures to put I-957 to a public vote, the most likely scenario is that the initiative will fail by a very large margin. We can then hold up the vote as a referendum on the premise that marriage exists for the purpose of procreation and thereby goad the Legislature into changing the laws based on that premise and in effect order the courts to stop using that premise in future decisions. This will not be as effective as getting I-957 passed -- the court precedent will still exist and could still be used -- but we will still consider it a win.

Gregory Gadow
Washington Defense of Marriage Alliance
http://www.wa-doma.org

This is what they are responding to:

The Washington Defense of Marriage Alliance seeks to defend equal marriage in this state by challenging the Washington Supreme Court’s ruling on Andersen v. King County. This decision, given in July 2006, declared that a “legitimate state interest” allows the Legislature to limit marriage to those couples able to have and raise children together. Because of this “legitimate state interest,” it is permissible to bar same-sex couples from legal marriage.

This ruling is asinine, and I can definitely see why extreme measures are being taken to counter it.

It could also imply, that the state would have a compelling interest in restricting birth control - if their goal is to promote procreation as one of their "legitimate interests". It may sound far-fetched, but with this ruling in place it opens the door for litigation by the fundy extremists to argue for that very thing.