I am just rewatching Hound of Baskerville and at the end John and Sherlock talk about the ordinary black dog of the restaurant that they didn't put down themselves. Sherlock doesn't understand, why they couldn't do it. Makes no sense after Redbeard, does it? So I guess they came up with that idea later?

Sherlock was looking for something he loved to comfort him and found the memory of his old dog...
Also, he recovered from it's death.

Oh I see...
Denial, presumably.
Or maybe he had genuinely forgotten about Redbeard, until Mycroft reminded him.

Davina wrote:

Or he says that, even though he knows exactly why they would feel like that.

This.
Watched Baskerville again yesterday - he looks understanding at first and says "I see" - when John says "no you don't", he then says "no I don't - sentiment?" - playing along with John's view of him.

Well, he had that sentiment when he was a child. He probably didn't deem it appropriate for a grown man to feel the same since his growing up had to do with getting rid of those kinds of feelings. Or he'd forgotten. 

But, to take a Doylan perspective, Baskerville was written before so what we're doing is shoehorning post hoc explanations.

I had made the connection that CAM may have been linked to Moriarty.
But I hadn't made the final jump that in killing CAM, Sherlock thought he had at last destroyed the network.

Not so sure on that...
And he didn't stop her, anyway..she just would have had to kill him, too!

If you want to kill someone and you see an assassin trying to kill that very person, the stupidest thing you can do is interrupt the assassin. 

The writers said somewhere that the Redbeard story was a dog that was put down and his parents made him believe that he went to a nice place instead and Mycroft teased him about it. Something like that anyway, it's in the empire podcast. 

Sherlock Holmes wrote:

After much debating on the forum over the past week, we finally got to find out who Redbeard was/is...it's Sherlock's childhood dog!

I was really really happy with that actually, but I was wondering...what do you guys think happened to Redbeard? Obviously something bad that Sherlock was upset over, which is why Mycroft uses it as a sort of reminder for him not to get too attached or emotionally involved with anything.

I've just watched this last night. The introduction of the dog struck a chord in all us dog-lovers. 

One thing I expected at the end, with the helicopter buzzing over head, and the scene switches from grown Sherlock to the boy Sherlock was that the flashback to Redbeard would show Sherlock doing something like putting the dog out of its pain himself--shooting it, even as a boy, in the way a cowboy might put down his injured horse. Takes guts to do that. Would it be believable? Maybe. It is Sherlock. As believable as Mary putting a bullet in someone she knows and likes. 

Sob.