Maybe we have vastly different experience and takes on the loud minority of vegans.
Just like anything that can define people, there are bad apples. You probably see "those vegans" all the time. They might be arrogant or might not fact-check some of their claims, doesn't mean they're wrong on the overall message. They might have some cult mentality, but I see it as a flaw of individuals. They'll still be obnoxious with whatever label they want to shove to others face, vegan or not.
From there, you have the option to just be vegan and not flaunting how morally superior you are or berate someone else for their lifestyle publicly. It's just a descriptor of your choice in what you don't consume (animal products), not some kind of monolith. The vegans who just calmly eating their vegan food without making a fuss flew under your radar.
Considering you said that the biggest deterrents are vegans, I assume you agree with the main points of veganism. IMO, it is a different matter than Christianity because most religion wholly depends on the faith of its followers that their god is the real one, the belief in the absence of strong evidence. The researches of the pro and cons surrounding veganism are still infantile and there are undeniable drawback from going full vegan. But so far, many compelling research say that reducing red meat consumption is good for the environment, which is in dire condition. So veganism is still a moral choice to make, especially if you also think killing animals are immoral.
Disclaimer: I'm not a vegan.
Hi, One Piece fan here. Yes, it's really long and really intimidating to start. I haven't watch most of the anime too, and never recomment others to watch it. I'm solely reading the manga (and live action).
I suggest waiting for the netflix anime readaptation that's in production now. Logically, it should have better pace and much less filler than the first anime. It's gonna be way easier to pick up than the first anime with its thousand episodes.