And the contractions involved are VERY painful, if you're not aroused.
They are if you are aroused as well, but you simply don't notice the pain.
Not true. At least not for me. Do you just mean guys?
Not sure about how other people's bits work, but when I was younger and still walking on the coals of a constant hormone fire, every moment, I used to force blood into it to help expose more nerve endings to stimulation and very roughly and quickly force a cum out. There was no arousal, at all, only forced tumescence. I always had an immediate relief of stress and it did not feel good, but it did not hurt either. Kind of like digging out an in-grown nail, you need to do it and there are benefits, but I'd rather not have to deal with it.