People develop their own content and are more than happy to share. As long as you give credit where credit is due. Which, I feel, is completely understandable and fair.
The issue of stealing content is prevalent throughout the internet, and especially in social media, because it is hard to catch when people steal your stuff. You may never even see it. I have seen even large companies get called out for stealing an individual’s content. Usually an apology is issued but that doesn’t make it right. It is probably safe to say that hundreds of people steal content regularly.
On one hand it is difficult to always attribute where you got a photo and there is a good chance that it has already been stolen from somewhere else.
On the other hand just because everyone is doing it doesn’t mean that it is something that you should do as well. If you choose to share a tweet or content from someone say “via @” so and so. If you share a piece of content from a share on Facebook, tag that company or individual in it. You are building relationships and the person or company whose content you are sharing will appreciate it.
Remember… you learned in kindergarten to share – not to steal.