Grammar: "Just because A, doesn't mean B"

This construction has been explored over on English Language & Usage, and there's an interesting and more thorough treatment here.

The bottom line is there's nothing "grammatically incorrect" about "Just because X doesn't mean Y", but there are definitely some peculiarities. Not least that we're happier with "mean", rather than alternatives such as "imply", "prove", "establish", "reflect", etc., which (grammatically speaking) are no different.

Having said that, this is more a question of style than grammar. But in that context it's worth noting that ELU has had at least three questions about the usage, so obviously people feel it's at least "slightly odd".

I think it's generally perceived as an idiomatic usage more appropriate to informal speech than formal writing. I personally don't think there's any real justification for that perception — but since it exists, the careful writer should take it into account. In short...

Just because the grammar is correct, doesn't mean people won't think it's "not quite right." If you don't want to distract your reader with pedantic side-issues, just choose a different form of words.

The logical equivalent of "Just because A, doesn't mean B” would be You should not infer B from A. I will leave it to the pedants to argue whether A does not imply B is a valid alternative.

Were you to say this in everyday conversation with the archetypal person-in-the-street, your (grammatically correct) statement would attract more negative reactions (as in "Oooh, hark at Mr La-de-da") than "Just because ..."

As others have noted, there are often grounds for breaking the strictures of grammar for deliberate effect.

I agree with the scond part of Iucounu's answer: Whether it's valid logic and/or grammar or not is pretty much irrelevant if it's in dialog. Lots of people use the construction. Indeed, I'd say that in many cases dialog must use bad grammar to be convincing. Like, technically if someone asks who is there the grammatically correct reply is "It is I." But almost no one says that. People say, "It's me." If the character is a meticulous English teacher, perhaps she should say, "It is I." ANy other character should say, "It's me."

All that said, I don't see anything wrong with the construction. I must disagree with the first part of Iucounu's answer. THe word "just" is not superfluous here: at the least it adds emphasis. I suppose in a sense you could say that every emphasis word is superfluous in the sense that the sentence would be meaningful without it. Like suppose I wrote, "A very old man walked agonizingly slowly across the scorching hot field." Sure, I could drop all the intensifiers and just write, "An old man walked slowly across the hot field." Or even, "A man walked across the field." The essence of the sentence is the same. But dropping the modifiers and intensifiers not only drains the color from the sentence but potentially changes the meaning.

Some say that you should not begin a sentence with a conjunction. I categorically reject that rule. Sure, a conjuction that comes out of nowhere, i.e. that does not connect the sentence to anything previously said, makes no sense. But there are plenty of times when it is perfectly logical to being a sentence with a conjunction. (Like that sentence.) And the alternative may be to either omit the conjunction, thus losing the connection, or to make an excessively long sentence just so you can "legally" include it. (See, I slipped in another one.)