i have a friend who was recently in this situation, whose mindset about social media is much like yours appears to be.

his arguments against displaying his personal life on FB and IG to such a degree, well-reasoned and understandable as they were - fell on deaf ears. when she went ahead and tagged him in 'in a relationship,' two days after a conversation wherein he explained to her that he didn't want to involve their combined f-list of 2500 people in something they were still figuring out for themselves, he lost his shit.

her reaction was to immediately delete her fb and send him a scathing text telling him that fine, she just won't hang out with him anymore so that he can enjoy the 'freedom he so obviously craves'.

end result: he caved. they're FB official. things are fine, i guess. personally, i took her behavior and manipulation as a warning sign, especially considering similar arguments they've had since they met (she noted them as 'official' on IG about two weeks in; she persisted in posting pics of him everywhere even though he never even posts pics of himself and explained to her he wasn't a fan), but he has decided it's worth it, and it probably is.

anyway, so no advice, really, other than to say that your feelings aren't unusual, nor are they wrong. you're entitled to them.

you might try the explanation he used with her; didn't work with her (but i have a feeling that has a lot to do with her particular psychology, for reasons too plentiful to get into), but it might with your gf.