why would life be impossible with different constants? ya, i know that some would prohibit life but others wouldnt prevent all life from happening. maybe a bit different from ours, but still life.
also, as for why our constants are perfect for life, i can think of a couple explanations/thoughts wich dont need an id:
we got lucky
we came into being to fit our constants so it seems like their perfect for us, but really were perfect for them. this is the most realistic and scientific method i can think of, its much like mokeles previous statement with the puddle.
maybe theirs not any other "universes" with seperate constants other than our own, and this is the only one with the only constants wich have their own reasons for being what they are our science just hasnt discovered them yet. i like this one too.And it can fit into the 2nd one.