We got the nearly the same problem here, but i live after the categorical imperative and that means, i do what i think that all the others should do too.
The reason, why there are only two (here its 2 big and some mediocre) parties with a chance is, that nearly everyone is thinking like you: too calculating.
Same shit here, but less advanced.
The two big parties use this fear to hold their power and fear is not the foundation of a democracy (which you actually do not have).
We never had a democracy in America.
We were never meant to.
What we have is a Representative Republic.
Although one could argue about exactly HOW "representative" this government is...what with gerrymandering and so on...
For example, in my home state of Pennsylvania, things are gerrymandered so badly that...
52 percent of the people of PA voted Democratic for their Congressman...yet, of the 18 representatives PA is sending to the 113th Congress...only 5 are Democrats and thirteen are Republicans!!
Because the republicans cheated and gerrymandered the Congressional Districts.
Gerrymandering, by the way, is a practice in America whereby the politicians choose their voters...rather than the voters choosing their politicians.
In practice, a district is made "safe" for an incumbent by packing his district full of his party's voters...and putting all the other party's voters into another District.
Practiced on a statewide level, Districts are created by the majority party in the State House...and voters of the minority Party tend to get "packed" into a few overwhelmingly minority-party districts (the district I live in is one such District) and the other Districts are basically made "safe" for the majority Party.
And these lines are re-drawn every ten years...by whichever Party is in power in the State House.
You can see how a Party perpetuates it's power almost indefinitely through dirty tricks like this.
No democracy.
Not EVEN "representative" Republic.