While it's generally considered grammatically incorrect to start a sentence with "because" in formal writing, it's perfectly acceptable and even common in informal speech and writing. The reason it's frowned upon in formal settings is that it creates a subordinate clause at the beginning of a sentence, leaving the main clause feeling somewhat incomplete or less emphatic.
In essence, it's a stylistic choice. Starting with "because" can sound less polished or formal, but it can also be used effectively for emphasis or to create a particular tone. The acceptability largely depends on context and audience.