He absolutely can live without it. How else did he get to be as old as he is now? Instagram is only a few years old. It just sounds like he's addicted to it, and I can understand your concerns - they're valid..but he can totally live without it.
In a nusthell, it sounds like you need to draw a line in the sand and let him know how you feel, and that you are serious about this. If you are truly concerned that he is going to spoil special occasions or milestone with you by constantly logging it into social media, you need to say something. He can't always have his head buried in a device if he expects to be in a relationship, no? Especially considering your privacy concerns.
Also the old pictures have nothing at all to do with you, sorry to say. (I do not mean this to be mean whatsoever, just to clarify.) My partner of 7 1/2 years brought this up to me as well and it didn't go well.. He was a very nice guy and had a good job, masters degree, was president of his fraternity - so he had different expectations on me in that regard. Short and sweet of it is that if I allow it, its ok. If I wanted to remove the comment or picture years ago, or the moment I received it - I would have. I think when it comes to things like this, you are nit picking to help your argument. Don't do that. I cannot stress this enough. Especially if you have this conversation with him. My ex used to do this and I felt bad for him because he always got side tracked from what he was really trying to say, and end up completely off target...we would end up arguing about something completely different in the end because he couldn't stay focused on what he was mad about - he would just pull shit out of nowhere to see what stuck. Don't throw out hypotheticals in a conversation like this - even if you feel it would help your argument.
Your issue is his over use of social media, his attention whoring (which has caused him to be hit on and have people say racy things) and you would prefer he wasn't as loud about sharing things, as you are concerned about his and your safety. Nothing more or less . All of this other stuff is just "fluff".
Seriously just sit down with him, and get straight to the point. No "fluff", no hypotheticals. Perhaps he'll hear you out and change his habits or at least be aware of them as a possible problem.