Buying a ticket from A to B to C, and only using A to B because it's cheaper than buying a ticket from A to B is no more dishonest, immoral or unethical than selling a ticket from A to C via B for less than the same flight from A to B. In the latter case the airline is manipulating their pricing to take advantage of market conditions. In the former case the customer is manipulating their travel plans to take advantage of market conditions.

I have no compunction about hidden city ticketing given the airlines' manipulative ways.

In an upcoming trip to the UK I need to hop onto the continent and home from there a few days later. I have purchased a r/t ticket from the UK to a city on the continent for about half the price of a one way. I have no compunction about throwing away the return in these circumstances.

However, be aware that if you make a habit of it the hidden city ticket Nazis may seek you out. Unlikely but possible.