"not the software's responsibility to limit us to only positive entries. Does any one else have similar thoughts?"

Your role also is to use the proper tools for their specific function and need. Mileage math is done in spreadsheets and calculators. Stated Values would be put into tax forms. You simply fill in what is being asked for. And not putting in negative, does not mean it won't do math. If you see Beginning and Ending, did you see if it then "does the math" for you? You might simply be overthinking some of this.

I see this often: just because a Form accepts numbers doesn't mean it works the same as a spreadsheet program. You need to follow the instructions.