He then proceeded to hit me. I don't know what to call it other than assault, I'm sorry, because that's what it is. Hitting someone hard is assault, it doesn't matter if they want it, that's what it is.
Assault is non-consensual and is intended to destroy the victim. Domination spanking is erotic, consensual and provokes a certain response in the sub. I'm sorry that you can't tell the difference, but that doesn't mean it doesn't exist.
If you believe that scene of mine was assault, then you must also believe that I assaulted my subs when I was spanking them. (As they begged me to do!) I reject that assertion and find it both ignorant and offensive.
What I'm trying to work out is why someone would wish to be hit hard with heavy objects like this for an extended period. What has brought them to this.
That is for OP to answer. In my personal experience, people have different limits, they tend to grow with time. Some people have higher tolerances, some people find they need more as time goes on because they get used to it. The drug analogy is not a bad one. And as with drugs, you do need to be careful.
You seem to have this idea that in scenes, people just go at it hammer and tongs without rest and then when it's over everyone just leaves. It doesn't work that way. There's an ebb and flow to it, the partners bounce off each other, and then there is tender aftercare at the end, which is incredible.
usedtobedomme is right that it takes a while to get the sort of 'lifestyle' relationship that she had. And also right that, at the end of the day, the dom gets the final say. That's really kind of the point, and if that's not for you then fine. But the sub always has the choice to walk away. In my experience, they're actually quite quick to do so if they're not being dommed to their satisfaction.