You are misunderstanding the purpose of the plugin. This is not some kind of Blackhat SEO tool. This plugins just automates your daily tasks and saves you a lot of time, nothing more.
Plugin is very flexible, so you can just find the SEO strategy that works best for you and stick with it. If you think that re-posting article on LiveJournal hurts your SEO, change the settings and post only small announcements and backlinks.
Usually people write blogpost/article on their blogs and then go with some promotion by sharing it on Facebook/Twitter/Google+/LinkedIn and reposting on Tumblr/LiveJournal for the people who read only those sites. That's why defaults are set like this.
PS: And yes, you are wrong. Google actually loves links from Social Networks (and yes, blogspot/livejournal/Tumblr are considered as Social Networks by Google).