Quite often I see someone criticise a design, a product layout, code or technique etc only to then have their “right” to comment questioned because they’ve not created something of equal measure – very much a “who are you to criticise this” type response.
You don’t need to be qualified to provide negative feedback on something, you need to be constructive.
If there’s a requirement for technical knowledge (eg. code examples or source on a site) but to be constructive there, you need to be qualified and understand what you’re talking about.
In short, always give someone constructive feedback. It’s not negative, it’s helpful.