Not anyone on here but people in general.
Person A: “I will buy [product X]”
Person B: “Don’t buy [product X]. You should get [product Y] instead because…”
Person C: “I’m concerned about your spending habits.”
Person D: “Lol you actually wasted money on that trash? What a dumbass. [Product N] is much superior.”
Person A: “It’s MY money. I EARNED it. I’ll spend it however I WANT.”
Like okay? 
No one is saying it’s not your money. There’s no SWAT team with submachine guns raiding your home and forcing you at gun point to put another item in your cart. It’s like speaking with children but they also pay taxes.
Are you really pondering why a person who just got called a dumbass might react defensively to people telling them what to do?
Well I gave three types of responses. And even then saying it’s your money and you’ll spend it how you want is such a weak and irrelevant defense lol
Response D is just insulting them though, response C is something you should only say in private to a close friend as it is essentially accusing them of being unable to manage their own finances which is a serious accusation even if you think it's true (imagine an overweight person saying "I'm having a pizza for dinner" and you respond "you should eat something healthier". Response B is less objectionable but is still unsolicited advice which is generally considered pretty rude (they didn't say "should I get product X?").
Saying "it's my money" is not supposed to be a reasoned defence any more than telling someone to go fuck themselves is supposed to be advice, it's saying "mind your own business" and "don't tell me what to do".