[Legate of Amon Lanc]

And I could add one thing quite many people misinterpretate from the moment the films come out; Saruman was NOT the one who sent the avalanche.

I guess the main problem was that in the films, Saruman did not want the Ring for himself in the first place, but he served Sauron. Thus, by sending Gandalf to Moria, he only brought the Fellowship to more trouble. In fact, even this doesn't make sense because had he been a servant of Sauron, he would have told Sauron about the Fellowship entering Moria and Sauron himself will see to it that some Nazgul stand in front of the East Gate in case someone gets out. But given the logic of the films, even Balrog could have been a servant of Sauron, or at least, he was definitely a "bad guy" and this was the main point.

I would say the best way of interpretation would be to say that blocking Caradhras from Saruman's part was either a way of getting rid of Gandalf as the dangerous figure of the good side (Saruman presuming that the Balrog would finish him) or we can interpretate Saruman's words "And what then, Gandalf? What if the mountain defeats you? Will you dare to..." as if he thought that Gandalf probably would NOT dare to enter Moria, and this would mean taking the remaining path: near Isengard.