Despite the evidence to the contrary, Huck believes that Tom is smarter than himself. Huck thinks that Tom is more worldly and experienced; Tom wants to experience the sort of adventure about which he has read and heard stories. The need for complicated plans over simplicity shows Tom's general immaturity; Tom wants to do things "right," but doesn't think about real issues like safety and necessity. Tom even comes right out and says what he believes:
...a square window-hole, up tolerable high, with just one stout board nailed across it. I says:
"Here's the ticket. This hole's big enough for Jim to get through if we wrench off the board."
"It's as simple as tit-tat-toe, three-in-a-row, and as easy as playing hooky. I should HOPE we can find a way that's a little more complicated than THAT, Huck Finn."
(Twain, The Adventures of Huckleberry Finn, gutenberg.org)
It's not enough to be stealing a slave and to have an easy way of doing it; Tom wants the danger and adventure, and Huck just blindly believes that Tom knows what he's doing. This shows Huck's trust in his friends; he is not willing to really argue against an unnecessary rope ladder, because he thinks that it will help them in the long run. In the end, Huck goes along with Tom's plans because he really wants to help his friend Jim, and he thinks that Tom's "intelligence" will make their plans easier. He is, of course, wrong, as Tom sees the whole thing as an elaborate game.