I’ve read this article about sitemap.xml. I’ve been using sitemap for my site and I know that it helps your site pages to get crawled and get indexed on search engines. From the article, it said that search engine spammers used the sitemap XML files to easily find contents for their scraper sites. The scraped pages usually show AdSense ads with which the spammers hopes to make money.
The article is rubbish! For one, there is no penalty for duplicate content...there is only a filter system for filtering duplicate content. Why would a search engine penalize you for duplicate content? That makes no sense, competitors would have a field day getting rid of competition. Second, sitemap.xml helps search engines crawl and index all your pages, the only way a sitemap.xml file can hurt you is if you have broken links in your sitemap or if you have bogus, unrelated links which is obviously an exploit. I did not read the entire article but I do not agree with the passage you shared and I wouldn't hold any value in it if I were you.