I have to admit I'm confused about unions

With the events surrounding Wisconsin and Indiana I'm getting more and more confused about unions, to the point where I don't think I even understand their basic premise. I thought unions were labor employees who form a solid coalition to negotiate salary, hours, physical risks, etc.

I don't understand why teachers need a union. When the union at the company where I work threatened to strike, (they had no intention of striking and evil management called their bluff) I, a non-union employee, had to train to do a union job in case of a strike. That job was a desk job not unlike my own, yet it was considered eligible for union membership. These are jobs that have zero physical risk, not even driving a company car. What I have seen time and again is that these union employees get paid much more than their non-union counterparts and get vastly more benefits, stock options, healthcare and 401k company contribution as well. There is animosity between the two groups. Because evil management are employees, too. If these jobs do not include physical labor under severe conditions then I don't understand why they are unionized.

Secondly, if the point of a union is to form this coalition to negotiate pay and everything else, then why do they need to pay dues? Their huge bargaining chip is that they will strike if they don't get what they want. So it seems to me like they could accomplish this without paying dues to the union. What is that money being spent on? To me is screams bribe money, or money used for extorsion purposes.

And if the point is to not get screwed over by management then what is stopping the management from forming their own union? What is stopping me and the rest of the peons in my department from forming a union against the managers in our own little section of the company? It seems completely pointless to me.

When the whole Rod Blago-selling Senate seat thing happened there was a lot of talk about the SEIU and who was communicating with them over who would fill the seat. Why? Is that who Blago was taking money from? If so, then why weren't they on trial?

Do we even need unions anymore? Shouldn't labor and employment laws cover whatever unions do? And if we do need unions then can we do away with making them pay dues? These stockpiles of money are making me nervous. Not just for Wisconsin and Indiana but for every entity that has a union.