I've already apologised for using that kind of language to describe her, it was unfair on a platform such as this. As for the second point, are you denying those sort of people exist?
An apology for using that language on this platform doesn't alter the fact that this is what you think of her, does it? I'll bet that's exactly how you refer to her IRL.
I've yet to meet a woman who uses men as 'sperm donors', and I'm in my 40s. If, however, I've been incredibly sheltered and that 'sort of people' do exist, why weren't you more aware of it when you had sex with your ex? After all, as 'that sort of person' is so ubiquitous, chances are she was going to be one of them, right? Or, erm, not.
You clearly have a very high opinion of yourself, too, thinking as you do that your sperm is so very desirable 
OP, if you can't like your ex, at least try to respect her. She's brought your son up alone (proof she's not 'certifiable', IMO). For the sake of both of your sons, show some respect to your ex and to women generally. Don't let them grow up thinking that women are all users and out for what they can get, and when they don't play ball, they're headcases.