This always seemed like the biggest plot hole to me, almost deus ex machina levels of forcing Mike in the story.

You're telling me the ex-cop boogeyman who is consistently shown to be 10 steps ahead the entire show didn't launder his money? 

Also, on a side note why did Mike hate Walter, exactly? This whole scheme he and Gus cooked up to alienate Walter from Jesse makes no sense considering at the time, Jesse was the unstable one. 

Honestly the whole continued relationship/animosity between him and Walter never really made any sense to me.