Because the bars are representative of the barriers people see to being pretty or accepted. In order to lower the bars you have to throw up into the toilet. So you get a wrong response if you don't eat or if you eat and purge, the only correct answer is to walk through the bars because they're not really there. This section (from the end of the sewers till now) is all reference to the ghost girl from the subway.
I understand what you were going for for a story and metaphorical perspective. That's how I solved it in the end, and it's actually a very good psychological puzzle idea. But walking through what very clearly seems to be a physical object goes against everything we've experienced so far in the game. I think just having a texture for the bars with collision off is.. strange. And not a great idea gameplay wise.
The way I solved the puzzle in the end was I began thinking, "Maybe I destroy the bars," thinking back to busting the boards with the sledgehammer. And because the swinging moves you forward, I just slid through while trying to smash them. Don't you think this might've been a smarter choice? By actually making the player feel like they're making a conscious choice and progressing, instead of.. Glitching out of bounds?