As mentioned many times before, the key thing of EIP is in

encouraging more of the behavior that we want, and discouraging the behavior we don't want

It's change of economic model that, simplifying it to something like "this post will get x instead of y" basing on a shift in rewards is wrong, because it doesn't assume shift in behavior (which should change because of shift of incentives).

Currently, user without SP could take advantage of bit bots, go to trending, gain reputation all that while having negative cost (i.e. earning on that), because selling SP to bit bots is just the easiest way to earn. With 50/50 it will no longer be that simple, because you could earn with your own SP by voting for good content as much as self voting or selling SP to bit bots.