[user_12345a]

The basement is part of the conditioned envelope and having a return air down there is important so it heats properly - you should have a little bit of supply in basement as well so it's balanced.
This being said not fond of it being so close to furnace - technically okay if combustion air comes from outside and no natural draft/chimney vent water heater near by.

Your basement should not be damp or have odors - both are symptoms of poor humidity control.
If it is damp in spring summer you should be dehumidifying in those seasons and making sure water is properly draining away from foundation with proper grading and down-spouts. You should also make sure where the house meets foundation is properly air sealed, in summer leakage from outside can be a major source of humidity.
If you control humidify well in summer, the foundation won't retain it into heating season and it shouldn't be a problem.

If you have or are going to add air conditioning, the basement return air helps dehumidify the basement -> sometimes to the point when it's hot enough outside and operating a lot it eliminates the need for running a dehumidifier.

 

[user_12345a]

@jas258. Yes, the basement odors get into the main house. It will be noisier in the basement as well, but the back-drafting is a bigger issue. The other returns may see a weaker airflow, meaning the air is not circulated well.

Basements should be heated a little bit - it's part of the conditioned space and helps reduce risk of condensation on surfaces. It also helps with exchanging the air in the basement.

If there are odors - that problem needs to be fixed, the air quality in basement should be same as rest of the house.

Return air in a basement as well as a little supply is normal.
May be a good idea to reduce the size or better yet close it and put a return further away from furnace though.

 

[user_12345a]

I recently bought an “air things” radon meter bc I am considering finishing my basement. So when I looked at the picture of the basement, I thought: “radon?” Not sure what sucking air in from the basement does, but I thought it was best to keep them pressurized. I don’t care what code says. I wouldn’t want a basement return to be open all the time. I’d at least want the ability to manually close it.

And then there’s maybe carbon monoxide and maybe even mold or whatever other basement nastiness that I’d prefer to move up the basement steps instead of getting sucked into the hvac for immediate complete distribution.

If there's carbon monoxide, there's a major problem and having return down there vs not will not make a difference with sealed combustion appliances.

If you have mold there is a major problem too that needs to be dealt with.

The basement is a conditioned space. It is not like a crawlspace or garage!
The pressure should be neutral with supply and return balanced.