Should I add link to copied text for SEO?

Should I prevent my users from ‘stealing’ my content by adding a link as a source when a text is copied?

I am just wondering, because I see a lot of spammy website using my content. If I would do this, I am afraid that those websites will now be linking to me (because of my source) and negatively affect my ranking / SEO.

What would you do in my situation / what is best for SEO?