A passport is also just a few pieces of paper. I don't travel abroad any more for various reasons (not saying that would definitely never change), so I haven't applied for one since my last one expired many years ago. I understand that the law doesn't recognise my ability to do what I otherwise could, if I did have one. All fine.
A driving licence is just a piece of paper (well, a card now). My freedom to drive is hugely important to me, so as soon as I was able to, I did the necessary to get one and now gladly reap the legal benefits of it. All fine.
Similarly, a marriage certificate is just a piece of paper which confers legal privileges, makes legal assumptions and demands certain legal commitments. If you want that, which I did, you need to do what it takes to get one. If you don't want or care about that, you should/need do nothing. All fine.
Just don't expect the government to be mind-readers as to your wishes and intentions and to allow you to pick 'n' mix the desirable parts of both (or even magically 'know' which parts a person would have liked, after their death) whilst reserving the right to eschew the less desirable elements of both.
In the same way, you can choose to commit to paying a year's expensive insurance premiums or you can make alternative decisions as to how to spend your own money - both options are valid; but what you can't then do is first approach an insurance company after your house has burnt to the ground and then seek to get them to pay to rebuild it for you.
I'm aware that a passport and driving licence are 'passive' agreements, in that you can just leave them in a drawer and ignore them if you don't want to use them, whereas a marriage certificate - because it necessarily involves two people's rights and privileges - is an active agreement; but nobody is forced to stay married for life if they later change their mind. You're perfectly at liberty to marry, have an unacrimonious divorce and still live together 'as married' for the rest of your lives, if you so wish.