lisab said:
I'm assuming this is in reference to a job application, is that right?
If so, neither one is acceptable, IMO. For one, I don't recommend beginning a sentence with "because". While technically correct, it's too casual to use on a job application. I'd advise something like this:
"My skills and knowledge make me a good fit for this field. <Add a sentence here that explains why your skills and knowledge are important.> Additionally, I would be proud to know my experience is being used to <cure lepers, or whatever>."
Because your suggestion sounds more articulate, expansive and enthusiastic, it is better than the original. It
isn't better because it avoids sounding informal by not starting with "because". Because, in fact, it's an answer to a "why" question, there is an implied "because" at the start of your alternative that we could replace without making it sound less formal:
"Why do you want to work in this field?"
"Because my skills and knowledge make me a good fit for this field. <Add a sentence here that explains why your skills and knowledge are important.> Additionally, because I would be proud to know my experience is being used to <cure lepers, or whatever>."
By your stated logic the original examples could avoid sounding informal simply by deleting the word "because":
1. Why do you want to work in this field ? We want to and know how.
2. Why do you want to work in this field ? We want to and we know how.
That doesn't work. The problem was not informality, it was that they are sparse and colorless; perfunctory.
The "because" issue is, apparently, about avoiding sentence fragments, which prohibition became misinterpreted as a prohibition on using the word at the beginning of sentences:
Somehow, the notion that one should not begin a sentence with the subordinating conjunction because retains a mysterious grip on people's sense of writing proprieties. This might come about because a sentence that begins with because could well end up a fragment if one is not careful to follow up the "because clause" with an independent clause.
"Because e-mail now plays such a huge role in our communications industry".
When the "because clause" is properly subordinated to another idea (regardless of the position of the clause in the sentence), there is absolutely nothing wrong with it:
"Because e-mail now plays such a huge role in our communications industry, the postal service would very much like to see it taxed in some manner".
http://grammar.ccc.commnet.edu/grammar/conjunctions.htm
I'm pondering that the original examples might be grammatically incorrect because they are technically fragments and not complete sentences. The question is: is a person committing a grammatical error by answering a "why" question with a sentence fragment starting with "because". Absolutely everyone does this and I can't find any rules online covering this situation ("because" specifically in answer to a "why" question). When I insert the implied "because" into your answer it still sounds vastly better than the original OP examples, despite now formally being fragmentary and incorrect, and I can't think of an answer to a "why" question where "because" isn't implied in the answer, rendering any such answer an implied fragment. In this context it never sounds fragmentary. There's no sense of the thought being incomplete.