Question: I applied for a position, and the company got back to me with an interview invitation. I accepted, the interview has been scheduled, and the time confirmed. Following this, I had a conversation with my mother who brought up a consideration about the job that didn't previously occur to me (it's location is less than ideal, if you're curious). I don't want the job anymore, but should I cancel? Is going ahead with the interview unethical, as it disrespects the interviewer's time? But I also don't want the cancellation to be a "black spot" on my record. 

Another consideration is that another company sent an interview invitation for the same time, but my main concerns are the ethics and my professional reputation.

Answer: 
Yes. If you are no longer interested in or available for a job, you should cancel the interview in advance. You are not offending the employer in any way.
I strongly suggest you to not to cancel the appointment and be there on time.

Cancelling the appointment is the adult thing to do, of course. However, you can't be certain if the HR department of the company is adult as well. **Yes, they can blacklist you only for changing your mind.** Therefore, in case you consider working for that company in future, you should go to the interview.

About the second company, you can ask them to schedule the interview for another date. 

Of course at the end you are the one who makes pro's and con's list and decide if the company worth preserving for future.