The major reasons why deletion of redirects is harmful are:
- a redirect may contain non-trivial edit history;
- if a redirect is reasonably old (or is the result of moving a page that has been there for quite some time), then it is possible that its deletion will break incoming links (such links coming from older revisions of Wikipedia pages, from edit summaries, from other Wikimedia projects or from elsewhere on the internet, do not show up in "What links here").
Therefore consider the deletion only of either harmful redirects or of recent ones.