You primarily receive newsletters you didn't actually sign up for? (stores you bought stuff off, etc.) That's the only way it's spam. But there are plenty of people who actively sign up for and appreciate them.
When every website uses black-design to "helpfully" sign you up for their newsletter without you noticing, it gets harder and harder to differentiate actual newsletters that I signed up for, vs plain old spam. When in doubt, mark-as-spam it is.
You primarily receive newsletters you didn't actually sign up for? (stores you bought stuff off, etc.) That's the only way it's spam. But there are plenty of people who actively sign up for and appreciate them.