But that's the whole point - if he had just used their connections to get started nobody would have made a big deal out of it. If he had just leapfrogged all the other talented candidates to get a place at the prestigious art college he studied at in NY (which itself he undoubtedly only got into because of his parent's connections), it would still have been unfair for other people who didn't have that, but within the bounds of 'normal' nepotism.
If he'd finished his degree, done an apprenticeship, then got a normal photography job at a magazine or something and after ten years then published his first book of photos, fair enough. It's the arrogance of dropping out of school, not having any work experience but still thinking your holiday photos are worthy of a book deal that grates on people.
Same with cooking, nobody expects him to be at mcdonalds flipping burgers, but if he'd used his parent's connections to get some work experience with Gordon at one of his restaurants, then done a course at culinary school, then a job as commis chef and worked his way up, it would be more understandable if he then got a tv show.
To use your analogy, it's like your DC doing 2 weeks as an electrician's apprentice with your mate and then saying 'Yeah think I've learned everything I need to now, I'm going to set up my own business.' In which case, yeah, everyone you know would be laughing at him.
The Beckhams weren't just content with him having a leg up to the first step of his career(s), they wanted to skip all the steps in-between as well and go straight to established star.
When lots of people who have talent AND education AND experience often never get there of course people will have something to say when someone who has neither jumps over them.