... if I was doing one of those martyr style cutting off my nose to spite my face protests, maybe... but as it stands, not playing the game achieves nothing. My point is made (as effectively as it can be) by not paying for it.
I don't agree, sorry I quoted the last part instead of all of the bits as I'm lazy
By playing the game, you'll be pinging their servers, downloading their patches and contributing to their internal numbers for players. By talking about playing this game you are clearly excited about you generate positivity around it online... and I presume when you have finished it or are playing it you'll continue to contribute to the online positive buzz around the game.
By playing it you'll be actively helping promote Rockstar's game and product, part of which is the online you don't like.
By simply ignoring the online component but focusing on the single player content, you're protest is heard in the only meaningful way it can be. By not engaging with the online they know that they have failed to convert you and the rest of the players who don't engage.
If you decided to forfeit this whole game you wouldn't contribute to their numbers at all and, if others followed suit they would know that they have a problem they need to address. But by contributing to their numbers you negate this and simply help make the idea of second hand sales less appealing to publishers*.
*that is of course assuming you source your copy from a one time buyer (who plays it once and then never ever buys another copy) and not just a re-seller who effective works as any other video game outlet.