You are conflating the marketing copy of the company with the intentions and motivations of the users. Just because something confirms your most cynical expectations doesn't make it true.
Ashley Madison has absolutely no idea whether any particular user, if they are married, is on there to do anything with their profile other than browse, or whether their spouse knows they are on there, or for that matter if a couple is browsing the site together as part of their joint fantasy life, or if they are in an open relationship, or a number of other scenarios that have no impact on you and really provide no basis for you to cast judgment about their motivations--especially in an absence of evidence.
See again, my cite to David Brin's article on addiction to outrage.