I'll admit that I used to manipulate people a lot.
Why did you manipulate people a lot?
I'm not sure I just felt I had to do that to persuade others to get my own way.
I'm glad that you have changed. It is bad to be selfish and take advantage of others. People are not going to like you as much if you continue on that path.
I don't feel that I caused anyone harm.
Even if you don't think that you harmed people by manipulating them, you can't know what affects your manipulations had on them, particularly down the line. If they realize later that they've been manipulated, they're likely to think negatively of you and it may impact their own self-esteem.