Some people say might tell John his faithfulness in the main is foolish, but in all reality it is his strength. His, “there„” although kind of a childish way to end a statement that is verging on the argumentativeis a perfect example of the man’s stubbornness and resolve. His statement here is not only the end to an argument he wished he would have said when Sherlock first told him he wasn’t a hero, but also with anyone who might as him why he would still trust and believe in, pretty much everyone else’s eyes besides his dead and a criminal. But not to John Watson. Never to him. Sherlock is his hero, the man who saved him from a dingy flat and a life that really didn’t mean much to him anymore. Saw special things in him and about him when everyone else saw a washed-out soldier and helped him in ways his therapist never seemed able.
I once read a section from an absolutely fantastic fic that describes John and especially John in this scene better than I ever could, and it goes, “There are things in this world that are considered strong…Sherlock can easily name thousands off the tip of his tongue—steel and titanium and alloy and diamond…but those are smoke and veils and shadows and nothing more. There are things in this world that are considered strong- And then there is John Watson.”
No matter what anyone else says or thinks about Sherlock, even, in this case, Sherlock himself, John Watson will always stay strong and always believe.