anyone who complains about an added optional feature should just stop talking and playing games right now. the only time a feature is bad is if it isn't optional or detracts from another portion of the game.

Examples
mutliplayer in skyrim would have been good, unless it would have had less quest ect for multiplayer.
multiplayer in ME3 was good, as it didn't kill anything in the main game and was optional

Yeah, this has been known for some time. But anyway, we can't praise or scorn Naughty Dog just yet. We need to all just wait a while before declaring this as a good decision or bad decision. Is the multiplayer is bad then we can say they made the right decision. If it's good, then we can't say that. But as of now, we just don't know.

I don't really understand why some are upset with this decision at this point. The only reason I can think of is because they just dislike multiplayer in general. While its understandable to dislike multiplayer, I can't think of any valid reason to wish it gone. The fact is its optional and you can play the game as is its not even there. You could make the argument that the inclusion of multiplayer means a weaker single player. That's really a weak argument and its really just guessing. No one knows what the game could have been without multiplayer.

You could use sequels with multiplayer and compare them to their predecessors without multiplayer. But that's not really an accurate method to judge the effects that multiplayer has on singleplayer. There are so many unknown variables with sequels that its impossible to know the effects of multiplayer without travelling to a parallel dimension where the game didn't have multiplayer so you could compare the two. Also consider that some sequels with mutiiplayer have improved singleplayers, while some have weaker singleplayer. Some of the best singleplayer games this gen have multiplayer. There really is no evidence to suggest that multiplayer harms single player.

this, and in addition i dont know why some people swear that making MP takes away from SP.  The MP in BIoshock 2 was made by a different dev team in a different country

See, that's just a bad way to do things.

(AI's are very annoying...)

If they include a zombie co-op mode, I really hope they take notes from left for dead. The adventure type game played really is more engaging than being in some confined arena or area.

It adds an additional level of spontaneity when the levels are so vast and open with little pre-decided gameplay. You'll never know when an enemy will show and what enemy it'll be. It adds an extreme layer of tension as you know you never have time to relax and take a breather, because is you drop your guard for one second, then the enemy could rush you. Also, with the larger maps, teamwork really becomes an element that people have to work towards. Unlike most co-op games that take place on arenas or rooms where you are always at a xlose distance from your teammates and you're always following the same path at the same pace.

With a formula like Left 4 Dead, you could potentially get abandoned by your teammates if they decide to push forward while you decide to go Fanboy and rack up extra kills. Next thing you know, you're 25% percent of the way to the end, while your team is 60% percent of the way done. Or maybe they think up an entirely new method of co-op better than Left 4 Dead, but that may be too big of a request for Naughty Dog.

You mean Bioshock 2, the game that is regarded as a subpar sequel to the masterpiece that was Bioshock? Mass Effect 3 that was by far the worst game in the series, even if you don't count the ending? Uncharted 2 is regarded as better than Drake's Fortune, but that's only because people wanted nothing but surface-value stupid fun. Which was what Uncharted 2 delivered in. Overall, all three of these series have taken an American turn after including multiplayer, by being louder and dumber.

Adding multiplayer can easily affect the singleplayer. Why focus on the singleplayer when you know people will spend more time on the multiplayer anyway?

We need an ignore button here

Call of Duty is a bad example. CoD is a Multiplayer with a Singleplayer just to teach you the basic skills. Altough I know two people who really enjoyed the CoD Singleplayer. But it is MP based.

Last of Us has definitely focused on the single player, so I don't think we have anything to worry about