People would get scared as hell, it would be bad for everyone.
you are equating "51% attack happened" and "everybody knows it happened". however, these are two separate events, each with it's own timeline. moreover, second event may even not happen at all if the first one is of limited scale. and if second event happens, it happens later, when all proceeds of the first event are already cached out.
Even so. I think everyone has much more to gain in the long run if all goes well with bitcoin.
The growth perspectives indicate greater further gains than the attack could generate now.
really? you truly think so? that's so amazing that you think everyone, in every bitcoin niche, has the same to gain and the same time horizon.
in fact, miners have no intrinsic long-term motivation at all, since the equipment they own today will consume more electricity than earn bitcoins a year from now.