I've been over this with him, and he does see my point, he seemed to let go of his "he's happier without the operation" attitude somewhat. The main concern here though is always money. He understands that what we are doing (blood tests, for example) might help us to prevent illnesses and more costs in the future.
Still, he's not ready to spend another $40 on an operation that he doesn't fully believe in after we just spent about $75 over the last two months for blood and urine tests, vet bills, meds, and flea treatment etc. This might not sound like large amounts to you, but to put in perspective: our cleaner who comes every morning to do the floors, gets $22 a month for it. He starts resenting the animals over these amounts, which is counterproductive.
Often in situations like this I offer to pay all from my own money (I earn a little bit more than him), but with the AC we just bought and dental work coming up for me, I'm also a bit struggling at the moment.
There are other financial strains involved as well, but I don't want to go into more detail here.
I will continue to bring it up with him, and if he continues to say no, I will eventually pay for it myself.