Without a doubt, guest blogging is good for SEO. In fact, guest blogging is white-hat SEO at its finest. But you should understand the meaning of guest blogging in the truest sense. It's only when you understand this concept clearly and know how to go about it that you'll be able to make the most of your guest blogging efforts.
Guest blogging is not article marketing or article distribution or article syndication. If you are cranking out low-quality articles one after another and getting them published, you are indulging in spam.
If you take guest posting that way, you should quit it right now.
Hope you understand. Thanks.