Seems like preventing drowning is a key reason to start early. That is why I started early for both of my kids. Too many stories about kids wandering into pools and dying to not take it seriously.
Yep, that's a big part of it for us. We go to the beach often all through the year and usually spend a couple weeks every summer at a lake, so we are around water quite a bit.
Apart from safety, I just know she'll enjoy water so much more in general after getting over the hump. I could be wrong, but my gut feeling is that the fear of going under is only going to get more ingrained if we wait, so it's better to do it now.
I actually wish we had been more consistent with taking her in the water from the time she was a baby. That seems to be the easiest path. Babies aren't aware enough to be afraid (it seems to kick in during early toddler-hood), so if you get them used to going under as a baby, then keep doing it regularly enough, you can avoid that fear ever developing in the first place.