Absolutely B12 should be taken by vegans. This is not something I would ever recommend against. There’s a difference between supplementing something you can’t get vs. supplementing out of convenience.

I take a B12 supplement daily and encourage all vegans to do so. Supplementing with B12 when there’s no way for vegans to get B12 isn’t the same reductionist science as supplementing Omega 3 because it’s easier than reducing Omega 6.

B12 is a necessity for healthful living while omega 3 pills are not (though I absolutely cannot disagree with their convenience) as there are other ways to achieve the omegas balance you desire. Reductionist science gives us this “convenient” pill to take (and market to us) instead of affecting the understanding of the industry (or individuals) into reducing omega 6s overall so everyone can be even more healthy.