'Because S V ~, S V~.' Is this grammatically incorrect?

Is it considered a grammatical error to place a 'because' clause at the beginning of a sentence before the main clause in an essay?

Have you been told that *you can’t start sentences with the word 'because'? This 'rule' is actually a grammar myth! In fact, it is just fine to use because at the beginning of your sentence – as long as you do it the right way.

Our teachers advised us not to start with because since they noticed we so often wrote fragments when we did so. Therefore, the guideline to not start with because began as a way to reduce accidental fragments in writing and ensure students used complete sentences.

In truth, you can start with because if you include everything a complete sentence needs:

• semantically, a sentence must contain a complete thought and not be disjointed
• syntactically, a sentence must contain an independent clause.

[from Erin Lebacqz; High Value Writing; the last two bullet points from other questions addressing sentences. For example, Is We embraced a complete sentence?]

.................

That's not to say that some teachers may not be aware of the acceptability of sentence-initial because.

There are also issues of style; while because might be perfectly grammatical at the start of a given sentence, a synonym (and this might be a phrase) might be an even better choice.