It's illogical in this sense: If the God that is in everything is not a conscious God, then you're using a meaningless term. And if the God IS a conscious God, then you're accepting the idea of a conscious God without evidence.
More importantly, the rules of science and logic demand that all assertions be backed with evidence, and that all existents have an identity. A God without identity is a non-entity and a contradiction.
Great post, I think you summed up the flaws of Pantheism/"god is everything" fallacy pretty concisely, although I'm sure it won't cut any ground with the Pantheists here. Unfortunately people just seem to caught up in mysticism, and the need to feel part of something greater than themselves to let this go.
Pantheism really was the natural evolution from the old world gods. People like to believe in shit, maybe believe when they die that isn't the end, or that theres something magical and supernatural going on, but with the old world gods, you really have to fuck your logic centers to buy into it, mostly because the people who invented them knew fuck all about the universe, and where often bigoted and supported slavery.
If you actually read what it says in the holy books, and not what the followers want to pick and choose and "interpret", most religions (Islam, Judaism, Christianity) have really dumb ass miracle stories, like floods that encompass the entire earth, people coming back to life, people being miraculously cured, when we know this stuff is impossible, and the only way people can actually buy it is because it happened in the way old past, and they can come up with some nicely fitting bullshit about why those things don't happen any more, and why god was happy to show himself to people in the past but not anymore.
Also there are alot of backward claims about the earth being the center of the universe, and the sun and the stars being different things, light being made before stars, and the heaven being in the sky, hell being in the center of the earth. There are plenty abhorrent commands in old god holy books too, like kill homosexuals, or its okay to stone kids to death or own slaves, so you get to avoid that aswell.
With Pantheism you get to keep all the warm fuzzy mysticism, without having to acknowledge any concrete claims about the universe or follow bullshit "morals". you're totally free to make up whatever religion you want and claim it to be true without reality getting in the way, and if you make it as nebulous as "god is existence" or "god is math and science", then you have nothing to claw at your intelligence to tell you to stop buying into the bullshit.
As of yet I still haven't seen a single Pantheist on this board actually define what claims they actually believe, although usually it includes some vague bullshit about order/spirituality of the universe, and handily includes/supports and personal preferences and desires the person may have.