The inconsistencies are pointed out when a particular line of reasoning is given as "correct", such as one suggested in the OP and a few others presented here. Basically, it is a response to someone already asserting their view is more sound.
People can have certain diets for various reason, sure. I don't make assumptions there, nor do I generally care. But we already have a lot of context in this thread, and that is what I am responding to. The very topic of this thread is consistency in one's actions, thoughts and feelings.
I am not asking for perfect consistency, rather, I am saying it is impossible, so people can get off the high horse.
People get defensive when someone else makes judgmental remarks about those with different preferences, as if they have some moral high ground when they may not have any at all. Unfortunately, a fair amount of people seem to need such a high level of consensus that they think other people merely making different choices is a judgment of their choice. In fairness though, some do imply judgment with their preference by how they pursue it or speak about it, but I also don't think all choices have equally sound reasoning behind them. The lifestyle choices you mention don't strike me as fully equal in terms of moral value vs simply being a choice. People can make arguments asserting a choice is "better", but then they leave their argument open to dissection.
The thing is, a fair amount of loud vegans/vegetarians come across as holier-than-thou, as if their food/product choices are somehow noble and not merely a preference. They use terms like "murder" and other pretty morally damning terms. I am saying they don't deserve any special badge of honor. I'd say that veganism/vegetarianism is not inherently more ethical at all. I wouldn't call it much of an ethical action or assign it much if any moral value at all. It certainly doesn't have nearly the same value or meaning as many other things, and at worst, I think it can serve as a distraction from weightier matters.
Basically, instead of perfect consistency, which is impossible, I am considering how one prioritizes values and distinguishes between a personal preference and something with a more universal moral value.