The fact that this conversation exists is proof that the word is intuitively pronounced with a hard G.
The only reason to pronounce it like a J if because the creator liked it - and the reason he liked it was literally because of the (copyright-infringing) similarity to the peanut butter.
He made a huge contribution to the Internet by creating the format, and he deserves it gratitude. Mispronouncing gif is not the best approach to that.