I think much of her negative attitude had to do with her misunderstanding of BDSM and the people involved. Sure, there are some jerks out there who will treat a sub like shit because they don't really want to be in a Master/Sub relationship they just want someone to beat up. People who are psychopaths do get involved just to feed their need to control and manipulate but that's not what the Master/Sub relationship of BDSM is supposed to be about and those people aren't the norm.
In any relationship you need to watch out for people who are out to manipulate you. Be wise and get to know the person before you get undressed and play with them. If you are a sub then have a trusted friend to help you determine if a Master is good for you. Remember to be wise in choosing who to meet with and who to give out personal information to but those are the extremes of the BDSM world.
Subs always have the right to say no. All subs need to be clear about their absolute no's. They need to understand what they are willing to take part in and what they are unwilling to do. If you are experimenting with the lifestyle do some research before going to a party and be open and honest with the host so they know how experienced or inexperienced you are.
In the general vanilla world there is a misunderstanding that masters are abusive and all subs are in an abusive relationship. This is far from the truth. In most BDSM or Master/Slave relationships there is some form of spanking, lashing, or pain involved but the pain is not abusive. Yes, there are plenty of news stories of abuse out there to scare people into believing all bruises come from abuse. True subs want the pain.
You have to remember that to each his own. Many people enjoy the pain of a whip striking their bare skin. This isn't an excuse to hit your loved ones because you feel like it. The Master/Sub relationship is a complex agreement that allows both parties to be in control. A sub in a true Master/Sub relationship has the right and responsibility to tell when they feel things getting out of hand. Masters will push their sub to go further and experience more pleasure but they don't take it to the abusive level.
My church friend didn't understand any of this. She didn't understand the difference between abuse that is degrading and a relationship that is loving. From the outside people may mistake one for the other. Even some new to the lifestyle subs may fall victim to a jerk masquerading as a true Master. Be wise in picking who you play with and who you allow into your intimacy circle. A real Master/Sub relationship can bring many rewards and strengthen your existing relationship.