Is it OK to remove backlinks to a free theme author and then ask the same author for free theme customization?

I’ve just got a comment from someone who uses Aeros. He asked for help because he was having some issues with specific plugins on his website. I went to his page and saw that he removed everything that pointed to me, the author of this theme. Especially, he erased everything in the footer.

Themes like Aeros are provided for free. Authors don’t earn any money with it. Backlinks to the author’s sites are the only, very little ‘thank you!’ from users. As donations are rare (I got about $40 for my themes and my work overall – not worth the effort, but thanks to everyone who sent me some bucks), at least a backlink to the theme author should remain in the theme.

Removing links may be OK under the GPL License – you may edit the theme in any way. But removing every link and information about who made this theme and then asking for free customization is a slap in the face. Please understand that I don’t have the time to help users that don’t want to contribute to my (spare time) work in any way. I know most of you do – but there are some black sheep in every flock.