Is it bad? Well apart from the excruiating pain for the woman (seriously, it feels like being punched hard in the stomach) it doesn't cause any long lasting damage.... unless it happens all the time. Then it can cause bruising, infections, and more pain for the woman (not to mention being turned off having sex with the man!).

To stop this happening, you might like to consider some different positions where your partner can control how much of you she takes. Woman on top is a fabulous one for this. Spooning is also an option.

Also, sometimes the penis hits the wall of the cervix because the man tries to penetrate before the woman was properly "ready" - when i woman is fully aroused, the vagina opens up and the cervix lifts, so there's less chance of injury.

It can cause scar tissue as well. And getting that removed, while it the procedure didn't hurt, the aftermath was not fun to go through for like 2 weeks, because you're constantly draining an icky liquid as well as dead tissue falling out.