I think everyone has a different opinion on this...just as we all do on any other topic.

I personally think it's fine to teach a preschool child to read; if the child is interested. I don't believe in keeping something from them (obviously things must be appropriate) if they can handle it.
When my oldest son was in preschool (age 4) he was able to read short words, and was reading books by January of his Kindergarten year. He is still an avid reader, and excels at it. My daughter, however, was never into reading books and struggled to learn to read; she's just moving at a 'normal' pace this year. Only this year did she begin to pick up books to look at and read by herself. It probably would have been a mistake to try to teach her to read early, because the interest (and ability due to an undiagnosed vision issue) was not there. My 3rd son, age 4 (5 in June) is on lesson 8 of Reading Made Easy, because he wants to 'do school' too, and he's interested in learning to read. He also loves to be read to.
I'm not sure why other people have a problem with teaching reading early, unless it's because they believe that's pushing. Lots of people like to have a relaxed school or 'unschool' philosophy, and that's fine....but just like anything else, it's a philosophy and everyone differs there. I believe that only you know your child well enough to figure out if he/she is ready; and we must keep in mind that every child, even within the same family, is unique and learns differently. I think the ONLY time it would not be a good idea to 'feed their curiosity' as you say, would be if it is a harmful or inappropriate topic/area, KWIM? Otherwise, I say go for it!
