will I regret not going to a “name brand” school if I chose UCSD for its environment?
no, unless you let the opportunities at UCSD go to waste, same as if you had gone to a “name brand” (ivy?) school
Brand is never regretted. What students regret is taking on more than the federal loans in debt (ie., More than 5.5k for freshman year.)
Prestige is an irrational emotion that drives people to do some pretty crazy things…like pay $80k for a commuter car, or $250k for a bachelors degree. UCSD is a great school. Go there and be happy 
No.
Thank you for the replies. I think I need to use my heart and head, and I’ve been using only one at a time and getting nowhere. Best of luck this year!
You will have the pleasure of reading your Philosophy (or other) text while lying on the beach, with inch-tall inward-gliding saltwater bathing your toes every ten seconds. Prestige doesn’t hold a candle to joy. And UCSD has plenty of the former.
While the kids at Harvard can’t find grassy quad seating fit for their khakis due to all the mud, you’ll have sun, sand and gentle surf to help you study. Just don’t read your Econ there, or you may fall asleep and wake up spitting out water at high tide. haha
Btw UCSD is a brand name :).
Although if the choices truly are Harvard or UCSD for philosophy, I’d pick Harvard due to the resources there (the libraries, alone, are a huge difference, but also the professors + the philosophy majors from Harvard go anywhere they want in terms of post graduation fields and careers).
But what people regret most is high debt.