First off congrats.
The piece you linked seems a bit sensationalistic, and as you said unverified.
Regardless, while marriage is indeed a personal relationship, it is very much a union that is a signal in relationship to the community at large.
On the philosophical / quasi legal level (and I’ll try and dig up examples if you want)
Frankly, I think a more traditional look at marraige (from various cultures, creeds, etc) isn’t so much as showing that you are using the state as some arbitor in anything, but you are showing the relevant community a new indivisible functioning unit / family relationship (and to at least some degree, property relationship) that is not to be messed with so easily. If you look at past examples even the kings, etc didn’t try to replace the families - they just killed the husbands off if they thought they could get away with it to start their own family or enslaved massive populations after wiping out the opposing armies (ex: King David and Bathsheba, The Trojan Women) - but it was never officially a sanctified act (the non slavery part I mean).
Other than that, if you are tied to any specific community, church, religion, family or something like that which you value I would see how their customs of marriage relate to how they want the state involved in it. If they are against it, it would probably be a good clue to actually start being seriously doubtful on whether you should get a state license, otherwise it may be a good idea just to do what is most practicle / harmonious to the situation at hand. Keep in perspective the actual community you care about first, not the state.
Also, what are the pros and cons tax wise, and can all of the benefits of a marriage license be arranged through private contracts done through some sort of estate attorney?
Tax-wise, claiming marriage is almost always going to be better - assuming you mean it to be a permanant commitment, particularly if you start caliming children as dependants. Still though see a lawyer for a more personal and professional look at this if this concerns you.