I'm not so sure I understand what's considered "mean spirited?"

"Marriage" in this context is a term of legality for a specific contract upon which: the parties are clearly identified; there are legal procedures in place to nullify or terminate the contract should there be mutual agreement to terminate the contract or one parties breaches the terms and conditions - especially important in the settlement of claims and child custody/support circumstances. In addition, there is quite a body of jurisprudence to rely upon for reasonable decision-making.

Laws are not casual things. When you make one, you usually find yoursself knee-deep in side issues you didn't expect.

The Amendment as written takes a cautious approach, recognizes that "domestic partnerships" can be state-approved, and that such state approvals can require recognition for the purpose of such things as insurance benefits, et cetera, and that these recognitions will be clearly identified.

It is not "mean spirited" to recognize that the jurisprudence of the marital relationship has had several hundreds of years' development and refinement - and that refinement has come with much angst, error, change and adjustment. This is especially important in a transitory society like the US, where what's "legal" in one place is "illegal" just over the state line. Matrimonial law is more "national" than just about any other body of law where states have primary jurisdiction, and the inevitable problems of estate-division, custody, support (and alimony), et al when partners change jurisdictions need a legal "history" for proper applilation in courts.

"Mean spirited" - NO. Being cautious not to legally create havoc in courts - YES. Until the consequences and ramifications are recognized and accounted for (so that COURTS and JUDGES don't make law from the bench), the Amendment appears to me as a reasonable accommodation.