What is a 'pernicious' wrong belief?

Under six major wrong doings (Abhithanani) in Buddhism, (i. matricide, ii. patricide, iii. the murder of arahants (the Consummate Ones), iv. the shedding of the Buddha's blood, v. causing schism in the Sangha, and vi. pernicious false beliefs (niyata micca ditthi)), > vi. pernicious false beliefs (niyata micca ditthi) is mentioned in http://www.accesstoinsight.org/tipitaka/kn/snp/snp.2.01.piya.html . What is the definition of a pernicious false belief and why is it considered such a severe offense to be in the same level as other acts?