If there is a form of atheism which could be labelled as fundamental, I would be a card carrying member of such a group. The fact is that there is no such thing as fundamental atheists which some like to claim there is. By definition, atheism is the position that there is no sufficient evidence to support a belief that there is a god. Atheism does not have canonical texts which every atheist must study and adhere to. No, such text does not exist and there is no fundamentalist in this aspect.
As for assuming the position of the opposition in a debate, many do take the initial assumption that the opposition is a fundamentalist. If the opposition found such position is absurd and/or not his/her position, many are happy to adjust the assumption accordingly. Obviously arguing against a fundamentalist position is much easier - the level of absurdity are just low hanging fruits. The position of "sophisticated" liberal theist may be trickier. They typically use convoluted word trickery to avoid facing the absurdity head-on and most would have been practicing such mental gymnastic for sometime already.
In many of the debates I have watched, almost no theist managed to define god. That makes a fuzzy target to aim the argument. One way to nail them down is to make them acknowledge the god in question is the god described in the old testament.
The difficulty is those new-age theists who believe in a really fuzzy imagination and acknowledge that the bible may be wrong. Many of them are actually logic-illiterate - unable to reason with sound logic. Hitchens treatment to these are really entertaining.
As for the accusation of "evangelistic" nature of some more out-spoken atheists, I would say this. I, as an example, felt the pain of the failure of education to educate modern citizens and enable them to get rid of the shackle of religious bondage. I am applaud to the continuous abuse parents subject their children by indoctrinating young minds with myths (myths are OK, but it is NOT OK to say myths are true.), superstition and threaten them with hell. That is unacceptable. A child is NOT a property of the parent. A child is a human being - may still be dependent at the moment, but nevertheless is a human being with the right to make up his/her mind about what kind of stupid ideas s/he wants to believe in WHEN s/he is OLD ENOUGH to decide. Baptizing a child or allowing children into church should be crimes punishable by law.
Here is the response of Daniel Dennett on William Lane Craig (a typical apologetic liberal theist, I suppose). Mine is here.