I really do despair of some of the ridiculous logic concerning double negatives in English.
First: "double negative = positive in maths so it must do in language too"
NO: -1 + -1 = -2
i.e. two negatives added together equal a negative result. Only when two negatives are multiplied or when one is subtracted from another do we get a positive. So where's the logic in applying it to English?
Second: when somone says "I aint got none", no-one really takes this to mean "I have some". Given this is the case, WHAT is the point of claiming it to mean this?
[IP [I' [INFL ai[NEGP]nt [VP t [V' [V got [NP none]]]]]]], where "none" is a direct object.
Fourth: Numerous languages worldwide employ double negatives as obligatory in many constructions, cf. "no tengo nada" and "je n'ai pas rien" (arguably a triple negative, depending on your analysis of "pas").