Because I wouldn't mind getting a PhD and end up at a B.Sc. job. I love organic chemistry, and knowing as much as I can about it is no burden.
Ah, that seems like me when I first decided to go to grad school. I love to learn (and still do). So why not go? Who cares if I don't get the highest paying job... it's all for the love of the knowledge right?
Unfortunately it doesn't matter that you wouldn't mind doing a B.Sc. job with a PhD... what matters is that you won't get employed to do a B.Sc. job if you have a PhD. Sure you'd be qualified (actually, overqualified) for the B.Sc. job and probably even do it better than some college grad with a B.Sc., but with a PhD you are now more expensive to employ. Why would a company pay you more to do a job that someone else can do for much cheaper?
You say, "Well I'll just tell them I won't mind working for less", but that just leads to suspicions as to how good you really are if you have an advanced degree but would be happy to do something "below" your level.
I'm not saying this is how it always is and that employment in chemistry is a big bleak mess, but from everything I've seen and read it does seem like a Catch 22.
After 5-6 yrs of busting your butt off, going through the ups and downs of grad school, feeling very unsure of yourself a few times a year, etc.. you might not want to be doing something that you could of easily done with just a college degree. I'm not trying to turn you off, but think about what part of chemistry you really love. I've always been told that if what you truly love is bench work then you should just get a masters. PhD's will eventually be expected to manage/oversee others and you'll have less bench time that you'd desire. If it's the bench work you love, perhaps get the masters, go out and get a bench job, and be happy. If you want more opportunities than just bench work then perhaps consider sticking it out for the PhD.