It depends - if I carefully screen tenants, clean up the property and take undesirable behavior seriously in my buildings, I'm likely to improve the whole neighborhood just a little.   

Unlikely unless you plan on doing something shady or not taking care of your properties.Your mortgage will make it undesirable to sue.

I saw some other duplexes but they are located in a neighborhood that is very undesirable.

Cons: Very high monthly payments would necessitate we rent out our ADU on our primary property which is undesirable because we'd have to invest a substantial amount to get it up and running, we'd no longer have use of it (we use it a lot for family and friends) and we are stuck in 30 day only market so the return is much lower than with STR. 

Will a lender (bank) look at my current debt when I attempt to purchase my first real estate property and see that I currently have a mortgage already (too much debt-to-income ratio) and as a result this makes me an undesirable client for them and more difficult to obtain that 2nd mortgage for my 1st rental property?

Even if the property is sold, seller's are faced with the undesirable position of where to safely and profitably store and invest the proceeds.

Be careful not to get lured in by cheap, low end properties in undesirable areas however.

I would like to see them put in more places like Nickerson Gardens Calif.Not drop them out in the Boonies, but in Peripheral areas away from the path of progress and away from the suburbs, and get the crime out of the cities.

This doesn't include running peripheral lines from the water meter to the home (extra cost). 

Maximize tenant rent by adopting dynamic pricing; reduce tenant turnover by upgrading, immediate respond to requests, retraining personnel to be tenant responsive and tenant friendly; eliminate undesirable tenants; upgrade property physically and cosmetically; convert from utilities paid to separately metered; evaluate prices paid for insurance, taxes, garbage, water, security, landscaping.