Professional only sites, like some for electricians that are out there, are really boring and not very useful. Nobody would post any more.
Instead of exciting questions like, "help my toilet is leaking" or "my CO detector is sounding, what do I do?" you would get pros talking to each other and arguing about issues of needle point theory, which nobody, even the posters, would really care about.
For example, we would start getting talking points like "Nibco 90s or some other brand?", or, "would you always turn the gas off in a vacant property if you smelled a leak".
I agree that some of the advice can be risky, and that's why we have the pros here to tell silly homeowners like me to shut up when we overstep the mark, but I bet even Grumpy would not really care if I started to do some gas work on my furnace in the house I live in at my own risk to save a few quid. He would start to care if I started to do some gas work in the house that I rent to a poor couple and their kid, to save a few quid, and here is the subtle distinction.
Incidentally, I have done my own furnace work. I replaced the board, door switch, transformer, thermostat and vent damper all without incident.