According to research about critical thinking in online learning, online forums offer the potential for critical thinking, problem solving, and active group participation similar to FACE--to-FACE classrooms (Al
Bunning (2005) The Role of Critical Thinking in the Online Learning Environment focuses on reflection, interaction, and feedback, not only to reinforce learning, but to raise learning to higher levels of critical reflective thinking. It demonstrates the value of interaction and learning communities to enhance quality and effectiveness of online learning, especially in problem solving and critical thinking skills. She provides an excellent example of how interaction online can enhance critical thinking with the use of "create a problem" exercise for students.
http://www.itdl.org/Journal/May_05/index.htm
Ramona Hall in her paper also provides a great review of critical thinking in an online environment.
In my view are such suggestions given in textbooks rather idealistic, critical learning develops best in direct interaction of controverse discussion with groups of students.