Yes. What's not ethical is delaying an easy checkmate to see how many of your Pawns you can Queen before mating your suffering opponent. A kid on the high school team I coached once did that against an unrated player and ended up stalemating him and costing my player a lot of rating points - karma at its best!
Ethics
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If your opponent lost his queen and you have the ability to queen a pond. You are going to win the game.
If your opponent doesn't resign you get to choose to queen the pond for an easy, secured, check mate or use your skills to mate him with what you have.(riskier)
It's not a matter of ethics in my opinion. The bottom line is that you played better and should win the game....so make sure you win.
Do it the harder way to practice your end-game or do it the easy way as to be prudent and avoid those occasional devastating mistakes we make as humans. If you do take the risk and make a mistake...in that case you should not get the rating points because you are a bit reckless and your opponent should get the rating points because he never gave up. 
This is my opinion.
Cheers
yes. your opponent played badly therefore it's ethical.