I don't think customs are a waste of time or effort, but some certainly do fall into that category. The whole ven diagram dynamic of some within being A and some being B.
I just think it's a tad objectionable (not overwhelmingly offensive, just... unnecessary and kinda snobbish) to go out of one's way to snub another's customs, whether or not they're wasted efforts. If you wish to help someone by potentially enlightening or educating them, that's one thing. But finding joy in eating a meatball in front of a vegan because you spite their choices is just being a dick. I've made the mistake of pointing out my joy of meat eating to acquaintances who were dedicated vegans, and even though I wasn't trying to push it onto them, they got quite offended anyway. I can't imagine how that scenario would've played out had I BEEN pushy and asserted my choices as superior to theirs...
On the flip side, I frequently and regularly inject myself into conversations because I find the discourse intriguing, and I do my best to keep my personal position (if I have one) as ambiguous as possible, because hopefully that won't color the bias of the other parties and influence them to, like the above, "make any points" and try converting me or anything. I'm just interested in the debate and the stances, after all. Yet a great many of those times, much to my continued fascination, the parties involved project an expectation upon me, and label me as such, because I ask questions. If I ask "why is it bad if they're gay?" that somehow makes me gay or bi. If I ask "why is it bad if they're religious?" that necessitates that I'm religious. Technically, the only things those questions necessitate are that I'm ponderous, and nothing more. But the act of asking them spurs many to form an opinion about the one asking, and they immediately begin forming biases against them for doing so. I don't get how that works, personally, but then I've come to the conclusion long, long ago that I'm one of the most open-minded individuals I've ever been aware of.
But I digress.
I'll eat some delicious barbeque because I enjoy it, and I think it's a sublime food, but not as any kind of showcase.
But it IS fucking delicious, that's without a doubt, and people who don't eat meat, or beef, or pork, are just missing out. Won't force it onto 'em, but I WILL think it a shame (to myself).