Okay, I'm going to pick apart the above post piece by piece, and I hope you understand it's not because I'm angry you disagreed with me, it's because I want to carefully explain why I think you're wrong.
You don't say what you think "the entire point of writing in first person" actually is
. For me, it's the deep-seated (not "seeded") immersion in a character, making yourself see the world as she sees it and tell it as she would tell it. This is a difficult skill, one of the hardest (but ultimately most rewarding) parts of writing. So it's a little hurtful to see using multiple first-person narrators described as "lazy" — because if done properly, if you create each narrator's voice and truly get inside their perspective, then making yourself do this multiple times within a story is giving yourself a lot more work to do.
I would guess that you meant "lazy" in plot-structural terms: a first-person narrator can only relate scenes they witnessed, so switching narrators is a "cheap" way to let the reader know about important events without having to restructure your plot to make sure the narrator witnesses everything. While true, I'd say again that the interest of getting to see things from a different character's perspective and getting to know that character from the inside, if written well, should outweigh this. Ultimately, it's the characters, not the plot, that make a story.
There is, of course, the problem with the "device" — how you justify multiple first-person narratives existing within a single text. You could have an epilogue explaining that the "primary" narrator (if there is one — in my works there always is) has compiled texts written by the other characters. However, I hold that since first-person narrative is an artificial device anyway (no-one actually remembers action, let alone conversation, in the level of detail required for a narrative) there's no reason multiple narrators should be any less acceptable than a single one. You, the author, are pretending your characters are talking. The reader knows this. What more is to be said?
I agree that switching narrators is never smooth, which is why I always do it over a chapter break, where you have a discontinuity anyway.
As for your last point, it's true that there is nothing first-person can do that third-person can't... but the converse is true as well, so that's hardly a valid reason to choose between them. Ultimately it's an aesthetic choice (well, novel-writing is an art form, so is that a surprise?). I prefer first-person because it gives me that sense of immersion and strong focus on a particular character. (Of course a third-person narrative can also focus on one character, but not quite to the same extent; even in something like Harry Potter
, the use of third-person gives you the sense that the world is what we're mainly interested in and Harry's character is primarily there to give us a viewpoint on it.) In a first-person narrative, the main character has to be interesting, likable and complex enough to "carry" the story, but if she is, then that automatically gives me a reason to be interested and involved.