Flojobunny - a couple of alternative wording options could be:
People with depression
People who experience depression
Also sufferers of depression - for the purposes of illustrating your assignment is not unethical or demeaning. It is a statement of fact not aimed at any individual, or with any malicious intent, so that isnt unethical.
Unless I have misinterpreted the reason you mentioned unethical.
If you are talking about ethics with reference to avoiding the anti-plagiarism software, here are some thoughts - I am doing a PhD so am up against the same challenge!
Provided you are rewording your statement to fit in with the 'argument' you are making (ie not copying it word for word from a text or online source) and also you include some relevant reference to any research that can validate your position (for example, "the study of depression in teenage boys by Jones and Jones 2009 suggest x and y") then that is fine.
You need to demonstrate you are bringing into your assignment existing knowledge to back up your argument, plus giving credit to the source, not passing off the research as your own. The argument you are being asked to make will be a blend of your ideas plus past knowledge.
It is a fine balance, and you are correct to think about it, that does not make you unethical, you are playing by the rules.