“Lifestyle” is a lot more than orientation.
Lifestyle involves what you do on the weekends, what you do on your days off, what you do to relax, what you do with your spare income, where you go on vacation.
“Celibate” is not a lifestyle. “Gay” is not a lifestyle.
“Hermit who lives alone with 37 cats and does not go out except to go to work and do the grocery shopping” is a lifestyle. “Monogamously partnered professional who has memberships at museums and a subscription to the opera” is a lifestyle. “Barfly who has casual sex with anyone who’s interested” is a lifestyle. “Jet setter whose relationships never last more than three years and whose kids are raised by nannies and governesses” is a lifestyle. You may note, at this point, that none of these lifestyles have anything to do with orientation.
So intentionally using the word “lifestyle” when what you mean is “orientation” is both technically incorrect—because the gay hermit who lives alone with 37 cats has a lot more in common with the straight hermit who lives alone with 37 cats than with the monogamously partnered gay couple—and misleading—because the stereotypical “gay lifestyle” is closer to either the barfly or the jet setter, and using the word “lifestyle” rather than “orientation” conjures up a lot of really negative connotations.
And no, if there was a legal status that was claimed to be equal to heterosexual marriage, I wouldn’t be satisfied, because unless it is the same status there is no way it is equal status. There are already companies in Massachusetts attempting to distinguish between people who are married to people of the opposite sex and people who are married to people of the same sex, so that they can deny insurance coverage (among other things) to the latter; I see no reason to create a separate status to make this even easier.
And “separate but equal” definition is entirely fulfilled by calling them different names, because they are different things. For instance, the argument can be made that California is required by the federal Constitution to recognize gay marriages performed in Massachusetts, because Massachusetts calls them marriages and they are the same legal status—just as Virginia was required, by Loving v Virginia, to recognize interracial marriages performed by the District of Columbia in part because they are the same legal status. You cannot make the same argument for civil unions, because they are different legal statuses.
It’s not merely vernacular. It’s a legal term of art. That is why it’s so important.
To use your analogy: you’re claiming that because the “candy” and the “bon bon” are the same thing, so the word used is irrelevant. I’m pointing out that there’s a big sign on that movie theater saying CANDY MUST BE EATEN IN THE LOBBY, and so long as I can only have candy while you get to have bon bons, we’re not very equal, are we?