In today's society, rough sex seems to be a trend that many have adopted. R&B crooners sing over sensual melodies about "knocking walls down", rap legends rhyme about "beating the p*ssy up" and men go round for round in the bedroom like Mike Tyson in the PRIME of his career pounding away at a woman's vagina believing he is making her feel amazing. Fact of the matter is, for the average woman, all of that hard pounding doesn't deliver pleasure, but on the contrary, more pain with each long, hard stroke.
I've heard men call women "weak" for "not being able to take the D", but what many men fail to realize is that (1) The average woman CAN NOT freak like a porn star (even some porn stars complain that it hurts from time to time) (2) the vagina can only take so much heavy friction before damage occurs (3) The vagina has an ending (4) when a woman flinches or says ouch during sex, she's SERIOUSLY feeling pain.
The vagina leads to the cervix which then leads to the opening of the uterus within the pelvis, so when a man is "drilling" trying to reach the "bottom of the vagina" by taking long hard strokes, he must realize that THERE IS AN ENDING and there are sensitive organs that can become damaged if too much force is applied. Rough sex can damage these internal organs and can shift things out of place (i.e. tilting of the uterus) as well as cause internal ruptures that can lead to blood filled cysts on the ovaries or within the uterus. Twisted fallopian tubes, tearing of the vaginal walls and vaginal opening, bleeding and swelling can all also result from rough play.
There are some women who need to be penetrated hard in order to feel any sensation within their vaginal walls, but those women have either experienced damage or trauma that has caused them to lose sensation (i.e. multiple rough sex partners, damage from child birthing, sexual abuse, mental disconnect) or they are into BDSM where pain arouses them and helps them reach a climax.
When entering into a sexual encounter, men must understand that sex is not a race and going hard isn't what will bring the the ultimate stimulation for most women. Being attentive to a woman's needs, going at a steady pace to ensure she feels the swell of the stroke within her walls, touching and caressing and communication are all keys to a successful sexual encounter. If she communicates that you're going too hard, too deep or too fast, switch of the depth of penetration and speed.
Don't let the popularity of pornography or the messages within music and media cloud your judgement. Put her comfort and safety first.