The vagina can accomodate childbirth, so fitting a hand will not "ruin" any vaginal walls if done right.
Not sure if you've been watching very extreme forms of fisting, but more sensibly done, there should be no harm.
The pleasure it brings? Well, for sure many women feel more pleasure from it than anal sex, as fisting is a very good, probably even among the best, way to reach and apply pressure to the g-spot.
I'm personally turned on more by vaginal fisting than anal sex, because I'm pretty sure the former is often more pleasurable for the receiver. I have also seen videos of women getting orgasms from this, and it's also confirmed by what I've read on the Internet about it, so I doubt it's faking. It's also often easy to tell a faked orgasm and a very strong one with accompanying "cramps". :)
You can read more about fisting here:
http://www.sexinfo101.com/as_fisting.shtmlhttp://www.soc.ucsb.edu/sexinfo/?article=anatomy&refid=015You may also wish to read input about fisting experiences here, and no one has really a reason to lie:
http://www.erotica-readers.com/ERA/ITEM/Fisting.htmSome quotes:
"I've been fisting myself for a while now, and always enjoyed it. Last
weekend I was with a partner who really wanted to try it for himself.
It only took him about 10 minutes with a little lube to get his whole
fist inside. That's the biggest hand I've taken inside, and it felt
wonderful. The orgasm I had was so intense that I couldn't speak or tell him
to stop or anything. After a couple of minutes I just had to push away
from him to stop. It was fantastic! So yes it definitely is possible and it's very enjoyable!" - Q_____________
"I am in awe, I want so desperately to be fisted. I have a guy who is
great in the sack and I think wants to fist me but doesn't know what
to do. I am waiting dreaming and juicing. He has tried in the past and
gotten to 4 fingers easily, I want it I know I can take it, just need
him to commit." - KellBell
_____________
"WOW! My partner and I have tried this and LOVE IT! I have had
children so it was much easier for her to fist me. Not only do I love
the feeling of her fist, but the emotional stimulus it gives me when
she is fisting me and looking into my eyes - that is where real orgasm
starts. I am working on her. She has not had
children. My hands are larger than hers and it is taking some time. She
must be relaxed in order for this to happen - and it will. Then I will
be able to make love to her like she does me. It is wonderful." - Cindy
_____________
But of course, as with many things, not everyone likes it! Many, many, do though.