It wouldn't. Why the hell can't I (or someone) randomly stumble on some post by choosing show me local (server) content feed or by choosing show me all, or simply by search and then vote up/down the post or comment even if I'm not right now in that particular comunity. E.g. if someone posts perfect or simply wrong misguiding bulshit reply, or then I find the post very usefull, or then comment is funny or on a contrary it's not. People are not living in a boxes of closely guarded comunities without exploring whats outside or new, without migrating, joining, leaving, fighting, agreeing, cheering, checking what ather users are into, etc..
And to add the second counter(s), technicaly is just as a simple as adding one aditional db field on posts table (or two if we keep ups and downs totals as separate fields now). And after, adding a simple if clause near the existing ones caunting global likes/dislikes, to increase a comunity counter too if this particular vote request comes from comunity member. Thats it. Then you can start expanding sorting options to enable more sorting options, but thats even not nesesary at first. Quite enough it would be simply to output vote count as a text at the top of post, near the global total - to be able to see what comunity members think and to be able to compare to what outsiders think.
Hard to not agree on this solid argument. That is indead the most blocking feature to use reddit without browsing frustration.