I agree in principle, and don't see why Rosberg should have backed out in general (a move around the outside is one to be respected, and no respect is gained from pushing someone on the outside off (Magnussen)), but realistically when the gap to Hamilton was stretching and Rosberg was only level with the rear wheels of Rosberg's fronts then clearly discretion would have been the better part of valour and he should have conceded. Over the previous lap he was much stronger without any obvious mistakes from Hamilton, so had that continued for another lap he would have had other opportunities, and aided by DRS too.
I can fully understand why Rosberg was angry after Bahrain as a couple of Hamilton's moves were inches from taking them both out in a similar way, and Rosberg had to dive off track a few times to avoid that, but to have it lingering on this long shows a lack of strength. If he's just manufactured that as a defense mechanism after the incident at Spa, or it's been brought up in team meetings since then that's OK, but if he's had that in his head ever since, it's a key weakness.
I don't for a minute think Rosberg meant to hit Hamilton. He wanted to make him think twice but misjudged the situation and clipped him, which has probably had the opposite effect (Hamilton knows Rosberg won't dare do it again, as either Mercedes will remove him from his seat, or the FIA will - Rosberg has no scope for mistakes in battles with Hamilton from now on). Rosberg didn't turn in on him (he was on the dirty line, the car was on the edge and he was correcting the car - you'll see it all the time in head-to-head combat, but it looks poor on a slow-mo in this ultra-scrutinised era).
There wasn't anything malicious about it, but was undoubtedly very clumsy. His manner in the aftermath sealed it though. Apologise unreservedly, accept full responsibility and hope others move on with you. Dig your heals in and you're making a rod for your own back irrespective of what others thought initially. I'm not sure he deserved to be castigated this much, but overnight he's become a global villain, and it's probably a good thing these aren't back-to-back races.... but if they're wheel-to-wheel again in Monza their reactions will be fascinating.