It's certainly true that sometimes people here do have unreasoning aversions to certain pieces of software that are undeserving of such ire. In the case of MacKeeper, it has a history of causing problems. Zeobit seems to have put a lot of effort into fixing those issues over the years, and so some of the reasons that people originally disliked MacKeeper are no longer valid.
However, there are still some ethical issues with regard to the company's behavior. They have been known, over the years, to give people compensation of all kinds for positive reviews. As one example, not long ago they offered their users free upgrades in exchange to posting comments on sites like MacUpdate and Download.com. (MacKeeper's rating on those sites went from one star to five stars literally overnight.)
They also registered a domain very similar to a product that competed with them in one area (clamxav.org, similar to the legitimate site clamxav.com) and posted a very misleading "review" of ClamXav followed by a big green Download button that went to the MacKeeper site. (That site is still there, though without the redirection to the MacKeeper site now. It's possible the site may have transferred ownership, but the domain is now managed by a service designed to hide the true ownership of the site, so nobody knows for sure.)
Given these problems, as well as the fact that most of the functions that MacKeeper provides are actually unnecessary, there are some very good reasons why MacKeeper is worth avoiding... whether all the folks in the "Anti-MacKeeper Cult" are aware of such things or not.