Why would you want to be friends with an ex? Who has time for that nonsense?

[Pepsi Plunge]

You're not wrong at all and hopefully, nobody who knows you (friends and family), will make you feel bad for not wanting to be friends with your ex or any future girlfriend you have who may end up being screwed up to you.
I'm older than you (I am 29 but I look younger) and I've only had 2 girlfriends but they were messed up to me.
Both of them told me that I can be "friends" with them but they weren't serious.
Why would I want to be friends with them though?
My first girlfriend whom I met in high school, dumped me because she liked another guy.
She went out with the guy she liked over me, not that long after dumping me.
I stayed nice to her for a while after she dumped me until she lied to one of her friends saying that I used to hit her and that I stalked her after she dumped me.
I'll admit to having a bad temper but I never lost it on her and I never stalked her.
I gave her a birthday present along with a birthday card that I wrote inside, saying that I didn't hate her.
She thanked me at all for the present and the card.
Months after this, we were together with other people one night at debate camp (she was one of my debate team members and I met her when she joined the team), she flirted with a guy from another high school in front of my face!
I ended up having a math class with her my senior year in high school but I ended up ignoring her.
She oddly said, "hi," with a smile on her face like a week before I graduated and I still ignored her.
My second/last girlfriend dumped me through text messages nearly 6 years ago.
I was with her for close to 8 months.
Despite telling me that I was her most mature/sweetest boyfriend, she never said, "I love you" only "I like you."
While I was her boyfriend, she was embarrassed to have me meet her family and kept me a secret from them (I did meet a few of her friends though).
She criticized everything about me, made cruel jokes about me to my face and would get mad often over small things.
She would complain about certain people and complain about things.
She lied a lot and was sneaky like keeping in touch with her ex boyfriend before me whom she told me about and was a jerk who she claim drove her to drinking and eating a lot.
She also secretly go on a personals site that she had a profile on to find another boyfriend.
Both of my ex girlfriends thought that I hated them and maybe I should've.
There's a great movie that I recommend that you might want to check out seeing someday called, "500 Days of Summer," if you haven't seen it.
The male character, Tom, ends up feeling miserable for a longtime over a girl he thought he belonged with who ended up dumping him.
He ended up realizing that he had to move on.
To me, I would never want to be friends in the future with a girl who may end up dumping me.
Telling an ex, "we can be friends," is so that ex who does the dumping, doesn't come off completely screwed up.
I'd rather keep my self-respect and just move on.
Again, you're not wrong in how you feel about not wanting to be friends with an ex and just move on.
Being friends with an ex is fine IF you and an ex mutually break up and the relationship wasn't horrible.
I hope that I've helped answer your question and take of yourself. I mean it. ~ Alan