He shared it with the FBI because he felt the American people should have been aware of it before the election.
The only problem with that scenario of yours is that, the dossier that Steele wrote has been proven to be a fairytale.
Here Are The 10 Most Important Reported Claims About The Steele Dossier On Russia
Far from being “verified,” the dossier is better described as demonstrably false. That includes getting basic facts about Russia wrong, making claims — such as the claim that Trump lawyer Michael Cohen met with Federation Council foreign affairs head Konstantin Kosachev in Prague — that are verifiably wrong, making cartoonishly outlandish claims about finances, and
There can only be one reason for disseminating false information about a presidential candidate, and that is to influence the election. A foreign national (Brit) that is trying to influence our election is in violation of our laws and those associated are co-conspirators. Just ask Mueller. Where is he in all this, by the way? OOOPS!! He is working for the Democrats now. LOL!! Muller and his hatchet man Weissman are working their asses off, as they may also be implicated in this whole affair. It has been recently revealed that Weissman was another point man for Bruce Ohr and his wife Nellie. You are obviously walking behind the wrong horse. Be careful that you don't drown in its manure.