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.
It is an interview and not confirmation that one has the job. Just like the employer may be very impressed with you, another candidate can walk in after you, and the employer feels that person is now a better fit. Therefore, if you are no longer interested in the position for any reason it is better to cancel and let someone else have the spot.