I guess tags are there because they fulfill a function, but if they aren't useful for your users it shouldn't be a problem to erase them, as long as you take the necessary measures not to get tons of nasty 404s, although if what worries you is duplicate content, you could just noindex the tag pages, I think most SEO plugins for WP have this option, else it shouldn't be hard to include the noindex tag in tag.php or whatever file generates it's pages, then you wouldn't have to deprive your users of an useful function (if that's the case, off course).
About your question of Google's preference, I'm not aware of it, but couldn't it be because there are many internal pages linking to tag pages and also with the same anchor?