What’s clear is that you’ll never get all developers to agree on what’s ethical, unethical, kind, unkind or whatever you want to call it.
Each developer has to do what he/she feels comfortable with and only he/she can make that decision.
What is important though is that this is not seen as a ClassicPress issue, as previously pointed out by @ozfiddler.
I would refer you to Plugin support and site admin credentials - #13 by timkaye which helps to clarify the position regarding the use of ClassicPress facilities (forums, Slack, GitHub) for plugin support.
I mention this in the context that should ClassicPress consider a plugin to be unethical, then it is unlikely that a) the plugin will be listed on the CP directory, and b) the developer will be permitted to use other CP facilities in relation to this plugin.