Is Grammar Obsolete?

I belong to several writers' groups. In nearly all of them a debate simmers below the surface: Does grammar matter?
The Pros' argument goes along these lines:  Of course it matters.  It's part of the craft.  Punctuation changes the meaning of sentences.  Poor spelling and improper word use stops a reader from becoming engrossed in the story.
The Cons' argument follows this tact: It doesn't matter if you use the wrong to or your.  The reader will figure it out.  Grammar Nazis are just snobby.  Grammer is obsolete.  I write and speak just fine, thank you very much.
So I culled some examples of error from a few different sources, including, but not limited to some of these writing groups.  This is just a casual culling from one afternoon.  I am not attributing anything so as not to embarrass and have changed any identifying words for the same reason.  I have left the errors exactly as they appeared.

• They were to philosophy what an American Team were to ...
• Your allowed
• Don't move to quick
• The human brian
• Math lab busted
• It has always bothered me the idea ...
• If a man needs rewarded ...
• Kindness is it's own reward
• For each and every authors ...
• It is a fantastic story how a woman falls in love when she less expect and he can’t let his ex-girlfriend go, they try to resist to find and accept that they are made for each other. 
• There is a mystery involving them, they don’t understand why they keep running into each other, but they are determined to find out. 
• Our black hairs blues eyes grandbaby is here.

Ok, so by the examples above, not unusual, or chosen for being especially bad, what do you think?  I think we need to pay a little more attention to communicating what we actually mean.