Sure, that's an option. A vegan should probably seek out another vegan to marry, rather than telling a meat-eater that she's wrong and has been conned by the system and that she's forcing you to buy some bullshit foodstuff that compromises your principles.
How is that equivalent? If I'm a vegan, I don't need to pressure others into my own belief system and expecting them not to eat animal food as well (I could, but I might as well not). Expecting your future spouse to buy a diamond that they think is an irrational purchase is by definition forcing your beliefs on others.
To be honest, so is not being willing to buy a diamond for your partner that wants it, but that's the point, find another person who agrees with your expectations of them.
