The question that needs to be asked...and answered before Bill 138 can receive serious consideration as a matter of equal rights is why (traditional) marriage has certain rights and benefits under the law in the first place. The government doesn't arbitrarily give out favors. It expects something in return.
The question is "what does marriage and the traditional family contribute to the common good that society has found worth incentivizing?) And since the proponents of Bill138 are asking for the same rights and benefits for same-sex couples, the corresponding question must also be asked "can same-sex couples make the same contribution?"
The government does not grant rights and privileges to married couples because two people love each other. Senator Cruz believes he can make this bill more palatable by making civil unions available to non-married heterosexual couples as well. But the question of whether civil unions should have the same legal status as marriage would remain.
In short, society has determined over the course of centuries that it is more cost-effective and beneficial for that society if the parents who beget children actually raise them. Thus we have (in the U.S.) the deductions for dependents, the child tax credits, the "married filing jointly", and other aspects of the tax code that incentivize the traditional family, and likewise the penalties for parents who neglect that family.
What the proponents of Bill 138 are missing in their appeal to the Equal Protection Clause of the 14th Amendment is that those protections apply to persons, not corporate entities, which any legal union of two or more people would be, regardless of what you call it. That's why a license is required, whether it is to do business or get married.
The government has a whole separate set of rules for legal entities based on the relationship of the entity to the larger community and its value in terms of the common good. Thus the queston: Can same-sex unions make the same contribution to the common good that married couples make (or at least are expected to make)?
Of course we are talking about children here. But since many people think we already have more than enough children, this aspect of the social contribution might be conveniently marginalized. However, such a speculation cannot negate the central fact that the survival of a society at its core is completely dependent on its replacement rate. This should be of particular concern to Chamorros who are fast becoming a minority on their own island. Other races are simply having more babies.
In European countries where the traditional family and marriage went the way of the Romans more than a generation ago, native Europeans are quickly finding themselves disappearing as Muslim immigrants are having 3 babies to their 1. It is predicted that by 2050 Muslims will be the majority population. Countries like Denmark and Sweeden are now paying their own people to have babies.
While, this discussion may seem to be tangential to the original question, it is not. Married couples and the traditional family fulfill a service to society by simply producing the next generation (the obligation to raise them is inherent). And while same-sex couples may believe they can provide that service via medical technology, technology can only manipulate life, it cannot create it. A man and a woman are still needed, be it only their sperm and ovum.
Thus only a man and a woman can produce the next generation without which there is no society - or perhaps a very different society. The fact that in some cases gay couples may make good parents does not mitigate the question.
An honest bill advocating for same-sex rights would take into account that gay couples, regardless of other attributes, are not the biological equals of their married counterparts and can never be. Thus, such a bill would NOT lay claim to ALL of the same rights and benefits that society has reserved for those who serve the special function of producing the next generation.
But that said, legislators need to examine the destructive elements within our legal system that reward irresponsible parenting and dissuade many from marrying and making the lifelong commitment to the very tough job of dying to oneself so that others might live.