Of course i would not make my child brush their teeth...i'm pretty shocked that everyone thinks that the right thing to do.
I think there are all sorts of ways to encourage a young child to brush their teeth without making it a "nonnegotiable"....my son went years with only occasional brushing...yes he had a couple of cavities, they've been taken care of, he's fine, his teeth are fine, and after his last dental visit he's made a vow to himself to be kinder to his teeth (he's 11.)
I think much of how one's teeth turn out is genetic....i brushed my teeth consistently as a child, went to the dentist twice a year like i was supposed to, had all the treatments recommended (flouride and all that)....and still have a mouth full of mercury. My son's father almost never brushed his teeth, and i think he's had maybe one cavity ever. Go figure.