Fair enough, no offense intended or taken then
I've also found that most designers are pretty helpful until things get to the point of someone wanting them to do their work for them.
I do think your comparison of critiquing photos isn't quite a fair one. You can look at a photo someone has taken and pretty directly critique it and suggest ways to improve it, comment on the way it was framed, lighting and exposure, etc.
A design concept may be just completely off, you may have a solution that's 180 degrees from what it actually should be. You can give suggestions, but it can be tough to critique that when it currently looks nothing like the end product should or will look.
It's also based largely on opinion, as bad as a design might be it's rarely "wrong" and I've watched even experienced designers defend awful designs. A photo can be obviously underexposed or overexposed, you might argue for the intent you had behind capturing the image but if something has the wrong exposure, is out of focus, etc., that's something that can be observed. (And yes, one can nitpick if something should be slightly one way or the other, but that's not what I'm referring to.)
As per the reasoning behind suggesting someone hire a designer, i think it largely depends on application.
Generally speaking the best amateur design effort is going to fall short of what a pro will do and most of time it's not tough to pick out. The same certainly applies to photography as well, but that amateur photographer isn't going to hire a pro to come shoot photos at the park for them. Someone designing or photographing for a business purpose often decides to "save money" by doing it themselves but ends up spending far more time and gets a substandard result.
