Formendacil, I permit you your amusement and my own.
But is that really what it is saying? Allow me to be pedantic, it does state that he simply entered then left either!
"I passed the Dimril Gate..."
I take it as passing across the threshold of one entrance into Moria, it would strike me as odd indeed,
"To poke one's head through the gate and decide that it's a very nasty place,"
as you put it. Especially in Aragorn's case, he does not seem to me the character who would conduct such a casual observation; does he not to you, create a person who would undertake a task properly?
Yes although there is no specific quote stating he passed through, I do not expect anythin less from him. As why Tolkien does not simply have him say so. I would answer that it was in context of Aragorn's character at the time. He does not reveal an awful lot, he is in conflict with who he is meant to be.
For he is troubled to take lead even of the Fellowship when Gandalf falls from the bridge in Khazad-dum.