The internet is a platform where many new media emerged and thus enabled a greater citizen participation in the production, publishing and sharing of media content. New, active and interactive audiences occupied space that was initially reserved only for professional journalists. When it comes to User Generated Content the user comments are “the most widespread and most popular type of communication on newspaper websites” (Ruiz et al., 2011), and it has a great potential as a place for public deliberation, which exists only when there are more users involved and their communication is interactive (Weber, 2014). Pavlik (1997) stressed that interactive communication is a process of reciprocal influence or control between journalists and citizens. This adds to Habermas' (1996) claim that for the achievement of democracy all participants, in this case citizens and journalists, should have the opportunity to communicate equally in the public domain. Readers' comments represent the most popular form of participatory journalism. Relying on Habermas, Dahlberg (2007) analyzes deliberative democracy as a set of ways of communicating in the public sphere and emphasizes that this communication must support equality among all participants and be as much honest as possible. Such communication that contributes to deliberative democracy must also respect the others and be empathic, arguments must be shaped so that others can accept the opinion of others or question their own. Depending on the media system in which information portals operate, the type of audience participation also differs, as do the characteristics of communication. Croatia belongs to a polarized pluralistic media system (Hallin and Mancini, 2004) characterized by homogeneous digital communities, weak pluralism of opinion, use of unacceptable speech, and lack of argument. Participatory journalism can be abused by spreading offensive speech that "harasses, threatens, undermines, attacks privacy, harms reputation and causes emotional discomfort" (Levmore, Nussbaum, 2010: 5). Hate speech is a far more dangerous than insults. The European Court of Human Rights in Strasbourg considers hate speech to be any form of expression that expands, promotes, promotes or justifies intolerance-based hatred, including religious intolerance. In order for a particular speech to be legally labeled as a hate speech, it must be about expressing certain hateful and insulting content and must be directed against certain social groups that can be identified by common objective features (Alaburić, 2003: 66). In this doctoral thesis, we are reviewing the development of news websites in Croatia with special emphasis on audience contributions through readers' comments. We researched the features of speech in these comments. Relying on recent theoretical research, we put special emphasis on some ethical issues in the communication of citizens on the Internet (Ksiazek and Springer, 2020; Strandberg and Berg, 2013; Ruiz et al., 2011; Torres da Silva, 2013). The research question that arises in this paper is whether the theoretical contributions of similar research in the world can be confirmed on the basis of research of citizens' comments on Croatian news sites. Qualitative and quantitative research methods were used to answer this question. The following research variables were set: to which extent were readers' comments marked with negative sentiment; does citizens mostly comment on negatively intoned article topics; to which extent do they use hate speech and hostility speech and whether other users condemn such communication; to what extent do citizens substantiate their claims with arguments. Comments were collected with the help of Vox Populi and Gephi tools in the period from 1 December 2018 to 1 June 2019 on the three most commented Croatian news sites 24sata.hr, Index.hr and Net.hr. 24,426 comments were analyzed using the big data research method, sentiment analysis and quantitative content analysis. In-depth interviews with the editors-in-chief of these news sites analyzed the perception of participatory journalism from the position of professionals and the extent of cooperation between professional and citizen journalism. The results show similarities with research of readers’ comments conducted in other countries, especially in the same media systems as Croatian. Hate speech and intolerance are most common when national topics are elaborated in news site article. The results of the research on comments also showed a lack of argumentative discussion and tolerance, which confirms the theories of Halin and Mancini (2004) according to which the Croatian media system shows characteristics of polarized pluralistic system. The research also showed the complexity of the relationship between professional and citizen journalism. This relationship is reflected primarily in various changes in way of doing business and in the increased expectations of the journalistic profession to protect the media space from unacceptable, discriminatory speech.