It depends what you're looking to do but there are definitely areas in north Minneapolis that have high Cashflow and aren't dangerous.

Buying with low or no money down and hoping that you can raise the rents in the future is a dangerous plan.

Demo, especially of old houses, can involve some dangerous materials - asbestos, for example.

I have done these, they are dangerous, but often the banks will not call the note as long as it is not rubbed in their face and no one is late with a payment or insurance policy or taxes. 

They call certain neighborhoods risky or dangerous that they know nothing about. 

Highest return on investment, but highest aggravation, is class C multifamily, in not great areas, but not in horribly dangerous inner city areas. 

My name is John and I was inquiring about your property at 123 Main.For the next several minutes, I was entertained by an explosion of every imaginable cuss word, how I must have been a scam artist, how what I was doing was illegal, and how I was taking advantage of people.

Anything over 30% is dangerous. 

I would be all in but it has to be the right place.Also, Cancun is now in the top most dangerous cities in the world.

The dangers of mold are greatly exaggerated by personal injury lawyers and mold remediation companies.