I'm gonna give a different opinion.

But he argued that flaunting them gave people the wrong impression and that I shouldn’t be “proud” of them

I don't think he's trying to be an asshole or controlling -- I think he found one of those cunts who cut only for attention, and he's scared of his girlfriend being judged as one of those girls.

There are, in fact, people who cut for attention. I knew several growing up -- I knew several who cut because of depression/anxiety and real reasons, but I also knew the ones who'd get scratches and cuts, and then start to do them on purpose, to then whine loudly about how "hard" their lives are. The main difference was shame -- one set was ashamed and hid it, but the others went well out of their way to try and bring attention to themselves. They're the types of people who also consider faking cancer for attention. It's not dissimilar to how people now use "trigger" to get attention to them not liking something, rather than people with PTSD who genuinely have their lives effected by a real trauma.

If my girlfriend went through an actual, difficult time where she harmed herself, I would never, ever want her mixed up with one of the liars. Her being confronted about being an 'attention seeker' -- I'd explode and freak out. I've done so with a friend of mine, who had been an actual cutter. Even worse were people who made fun of her for her legitimate emotional distress at the time, and not over mixing her up with an attention-seeker. Those were even worse, and she went through a lot of difficult times as a result of people like that.

Is the boyfriend going about this the right way? *Abso-fucking-lutely not.** *

But if he was genuinely good to OP, genuinely helped her feel better -- I'm hoping -- so, so hoping -- that this is a case of putting the most stupid foot possible in your mouth, and not realizing your fake excuses are worse than genuinely talking about what would happen in a terrible situation with other people. A case of, "Better I'm a bad guy, since you forgive me, than a stranger, who you will genuinely listen to."

Only OP can decide of this is a possibility or not -- but if it is a possibility and he isn't just an asshole, I would suggest a long, long talk, asking him what he's truly afraid of happening, and then going from there.

If my version isn't incorrect, and you can afford therapy, I would highly suggest you take him with you, OP, so that he can speak to someone about a healthy way to react to others being dicks about such a situation.