Is it entirely acceptable to inflict personal harm because it is “for the good of society”? While some forms of freedom of expression cause society as a whole to develop and recognize truths, other forms can be harmful to individuals. Mill discusses hate speech in On Liberty, which he refers to as the harm principle. This principle, Mill asserts, is the only exception that restricts freedom of expression. However, when this topic was briefly discussed at a conference on September 20, 2011, under the theme "Should Harmful Ideas Be Suppressed?" Mill's theories have been said to assert: who decides what is harmful, and that harm itself should be open to debate. As the topic of personal harm is debated, some forms of hate speech may be considered acceptable. Perhaps some forms can be allowed as long as they are not physically harmful, but mental harm remains.