You are a spammer
Spam is permissionless mass mailing. If someone has Liked a friend's band on Facebook, they've given permission for contact. If you're just not a fan of self-promotion, fine, say that, but don't claim that something's spam when it is nothing of the kind.
But there are different expectations for social media, where you expect a bunch of fluff. The whole point is that you've signed up for unsolicited bulk nonsense. I'm not sure what the difference is between someone who just posts a bunch of "come see my band" posts, and someone who pays to promote a bunch of "come see my band" posts.
So for promoting bands on social media, what I would is provide interesting content to the broader audience, like if we made a cool youtube video, and then be sure people knew where to find information about shows, I.E. the event pages for those shows.
However, I did creep into the world of spam from time to time: I would post unsolicited posts on my friends walls about really important shows. However, I did this very carefully, posting it only on my friends walls who I KNEW were strong supporters and wouldn't mind. This increased visibility without annoying anyone too much.
But it was kind of spammy and I'm not here to defend myself on how I promoted local art and made a living. I think spam comes down to intentions and being open to feedback: if you don't want to see my messages anymore, I would stop sending them to you IMMEDIATELY, including sending you event invites , and excluding individuals from those used to be really hard.