That isn't a good justification to me.

You want developers who spent years studying design and development, to spend months developing an app, to just give that app away for free?

People like you are why more and more developers join big corporations for salaried position rather than trying to make it by themselves in the indie scene. Because they know they can't make it in the indie scene because you are too cheap to pay for their apps (either by buying the app, or by consenting to see ads)

If your app can't exist without ads then I don't believe it should exist at all.

Sync for Lemmy exists as a paid, ad-free version. The ad-supported version only exists for people who don't want to, or can't, buy the app.