Why would you behave ethically towards a company that is anything but?
The slight remorse I feel by not using official YT frontends is towards creators I enjoy watching, who I try to support via other means, if possible. But then again, any creator or business who chooses advertising as their only business model doesn't deserve my support.
Advertising is a scourge on humanity. It corrupts every medium of information by allowing sleazy middlemen to psychologically manipulate one party not just into buying products out of manufactured desire, but into thinking and behaving in ways that serve someone's agenda. It is weaponized via platforms built by adtech companies, which have played a major role in the current sociopolitical instability in the world. It is so insidious that even though it has concentrated incredible amounts of wealth into the hands of a few, most people see it as harmless because they get products and services for "free". To hell with all of that.