Why in the world would you suggest deleting these pingbacks??? These are the links you built to your site. Find the best way to make use of them...
I'm not to familiar with the plugin Spam Karma, but if it works to reduce spam great. There is nothing more annoying than blog spam, but for those of us who have outsourced or used programs like Scrapebox for junk blog comment links... "what comes around goes around"!!!
I wanted to add my 2 cents and some input on the initial question about pingbacks and the thousands of links from article marketing. Pingbacks and trackbacks are Wordpress's inbuilt system to notifying blog owners when links are passed in between user blogs. These pingbacks and trackbacks are great for natural links if you desire to put in the time. For example when you link to another blog from within your post (i.e. content curation, or just a thumbs up for a blog you really like) you can create a trackback letting that blog owner know you linked to them, with hopes they will link back to you... "natural linking"
The pingback is a notification that a blog has linked to you. This is an opportunity... DO NOT delete these. In the comments section of Wordpress you have approved, pending, and not approved. Approved will show up in your posts, pending just sits there in the database really not doing anything, and here is what to do with the not approved. Filter all the comments by comments first... then clear spam. You are left with the pingbacks, all the blogs/articles with links to your site. Select all and click Not Spam, this will simply move all these pingbacks to your pending comments.
There are a couple plugins to help manage these pingbacks and for GOOD reason. Pingbacks are your proof of backlinks from other blogs. The one I use is Pingback Optimizer which will group your pingbacks into groups and submit them to RSS aggregators, which will help get these links indexed. You can also use Pingback Optimizer, and in my opinion the biggest benefit, to download ALL these links to a txt or csv file for further use, such as submitting them to BacklinksIndexer. There is also another plugin by Konrad Braun, I think it is called Ping Automatic.
We spend way to much time creating backlinks to just let them disappear into cyberspace. And remember a link that isn't indexed is really just a waste of a link. Keep track of these links and use an automated system (to save you time) to increase the likely hood of these links getting indexed and passing that link juice to your site.
Cheers
Doug