Why Moria?

[Rhod the Red]

"what about a sea route to the area of Andrast using an elf ship"

I have a reason why: It would mean that as the Fellowship would approach Mordor, it would be near the battle-centers bewteen Gondor and Mordor. It would not have been safe.

Crossing through the Misty Mountains, while hoping that Gondor would receive the brunt of Sauron's forces, was safer than travelling by the sea on the Southern shores of Gondor.

[Selmo]

Elrond rules out taking the Ring to Cirdan at the Grey Havens because it would be too dangerous. Frodo and the rest had only just made it to Rivendell and taking the Western Road back through the Shire to the sea would be anticipated by the Enemy; the road would be watched. Elrond was answering the argument that the Ring should by taken by sea to The West but it works the same for an attempt to go to Gondor by sea.

Also, Gandalf seemed to think it was very important to pass though Lorien, though he never gave his reasons.

[Legolas]

'That I feared it too,' Aragorn answered, `but less than other things. I knew the risk of snow, though it seldom falls heavily so far south, save high up in the mountains. But we are not high yet; we are still far down, where the paths are usually open all the winter.'

Aragorn says the risk of snow lessens in the south, and at lower altitudes. Therefore it can be logically deduced that risk of snow is greater in the north, and at higher altitudes. I wouldn't call that nonsense or speculation - it is inference.

It is illogical to think that Gandalf, Aragorn, the Fellowship, or the Council of Elrond were not thinking of risks. The whole route is planned for speed and avoiding danger as much as possible (which is why they don't go further south by the Gap of Rohan). Aragorn uses the word "risk" in the comment at the top of this post.