My opinion is  -  purchase cost, selling price, fees incurred through eBay/PayPal = net profit/loss.

It's not so much whinging, as you call it.  It's a case of facing up to the reality of whether it's worth pursuing selling on a platform that takes more than what you bring home.

And I agree, you are entitled to your opinion, but doesn't that also mean that others are entitled to theirs - which they choose to express on this forum.