Sure, it's a community concern. This gives neighbors the right to express their concerns and offer advice and help, not to overbearingly insist that work is only done by "professionals" who magically bless the situation.

Legally, it's generally commercial activity (eg contractors) that is regulated. Thus, after you've talked to your neighbor about best practices for mitigating lead dust, you've effectively exhausted your options. After that point, not "letting" them DIY will basically consist of harassment.

I used to own a property management company and I have overseen multiple home remodels (while doing one largely by myself right now). Hazardous material management on a work site are not somehow beyond regulation because it's not "commercial activity", that's preposterous. Homeowner-executed projects can be stop-worked just like everything else and hazardous material management is a standard part of code enforcement.

As to your postscript--yes, clueless or careless DIYers probably need the hammer swung at them, and hard, when they do something to create negative externalities. You have the right to not be poisoned by your neighbors. Even if they make you sue them to enforce that right, that still isn't "harassment", and it is genuinely and deeply gross to characterize it as such.

These things obviously vary between jurisdictions, but from my own experience lead-painted material is not "hazardous" waste. In fact, last time I checked (~10yrs), the official guidance was to put it in municipal trash or a standard dumpster. Furthermore, I've had an inspector called on me while helping to paint a house, precipitated by a busybody neighbor. The inspector established that we were family, and then just left never to return - lead exposure is regulated as an occupational hazard, and none of us were being paid. And my experience is from a state known for overbearing regulations.

I got rid of the PS because it was needlessly obtuse. But trying to restate it nicer - coming at someone DIYing with the attitude that they should be hiring "professionals" instead, as opposed to offering constructive criticism and perhaps even help, is a guaranteed recipe for a failed interaction.

And unless you've got actual demonstrable harm from your neighbor's activities - more than a vague worry about the possibility of lead dust being carried by the wind - filing a baseless lawsuit is indeed best characterized as harassment. At a certain point, there is an threshold of blame that is impossible to adjudicate. Slightly elevated environmental lead is squarely in that territory (it could have also come from a piston plane flying overhead), which is why the real fix is to systematically eliminate the use of lead to begin with.

I'm sorry, can we go back to the part where i "don't let my neighbors" do something? Unless they are in violation of a law that is actually enforced by someone, I don't think I have standing to let or not let them do anything.

In American jurisdictions of which I am aware, there are such laws around handling hazardous materials (and lead, especially in particulate form, qualifies). In hypothetical places where there aren't, the concept of a tort still exists.

You do, in fact, "have standing" to not have your neighbors poison you. This is a good thing. It should be celebrated.

In which you have convincing demonstrated that libertarianism and lead poisoning are locked in a mutually-sustaining cycle of brain damage.