So I looked up the definition. I thought that was the best place to start.

Spam: irrelevant or inappropriate messages sent on the Internet to a large number of recipients.

Since there is a NO way to qualify SPAM so that everyone agrees, I would agree with your statement that all social media is spam and even goes as far to say that all content on the internet is spam (at least in the eyes of someone, somewhere).

I think most people would agree that about certain messages, posts, tweets, etc being spam. But when you press in on niche topics, someone might consider something spam that I do not.

For example, posts about cats don't do anything for me, but there are people that eat up that kind of content.

Nothing wrong with a whole list of people receiving cat pics (if they signed up for it). But I will choose not to!

So for me personally, if the content is spammy I don't mind as long as I have a way to go on hiatus (either short-term or permanently).