My beef with the lack of a clamshell isn't the vulnerability of the screens but the size of the damn thing. The 2DS just isn't pocket friendly. The GBC and GBA didn't have clamshell designs but at least they were small. This is more like the old brick Game Boy but that was big entirely because of technical limitations of the time.
The screens aren't protected AND the system isn't all that portable. That's two big strikes against the 2DS design.
Given that the 3DS doesn't fit into the pockets of the target audience I don't think that is a strike, much less a big one, against the 2DS. For much of the rest of the potential audience it would be a house handheld so it doesn't matter either. If someone cares greatly about protected screens and pocket portability there remains the 3DS and 3DS XL.