In all fairness, I don't think it's that big an issue since you're providing free traffic/exposure to their website. I'm not sure why would anyone have an issue.
If you go by paper, lot of things can be an issue but that's what happens on all social media. People copy/paste and share.
You will need some very strict moderation to watch every single thing that gets posted. Not something doable for any website (including reddit which is one of the biggest platform).
If someone is sharing a content that can be helpful to others (assuming they're providing source link), I don't see a reason why they shouldn't get up vote.
but if someone is reading the full article on your blog they have no need to view the original. yes it's difficult to police but it is still a breach of copywrite and the author of the content is well within their rights to ask you to remove it or take legal action.
But aside from any of that it's not good for steemit to be full of unoriginal material and seeing as we all have a vested interest in steemit doing well, it's best to avoid copying full works and putting your own voice to the topic with quotes and links anyway.