A blank sheet or paper or empty screen can make things worse when someone has a bad case of writer's block. The opportunity to appear before an audience can heighten fears of making a fool of oneself. Whenever Web 2.0 tools contribute to decreased student engagement, it's possible the tools are no help with coming up with something to say and the courage to face the consequences of having said it.
A majority of people rank "public speaking" as their greatest fear. It's likely each has internalized nightmare experiences of getting teased, shot down or embarrassed in front of others. Survivors of abusive relationships are ashamed of exposing their thoughts or feelings. They believe they are mistakes that are not worthy of respect, not one of us humans who make mistakes.
When I've provided a preamble to students about to deliver class presentations, I attempt to de-escalate the adversarial context that fuels their fears. I remind them how school typically penalizes them for making mistakes and how learning to do things better only occurs by making mistakes. I offer them the choice of appearing perfect from the git go or appearing dedicated to further improvements. I suggest they can cling to their past history or let go of it to face the opportunity with less familiarity. I'm deliberately creating a context that supports risk taking, tolerance of imperfections and getting better ideas "for next time" after the presentation.
Web 2.0 tools may be getting offered as course requirements without any supportive context. They may "stare back at the students" like a blank sheet of paper. They may look as bad as standing up on stage in front of a hostile crowd. They may stir up lots of bad memories that inhibit self expression, sharing with others or learning from classmates contributions. In these cases, the "tools for engagement" could easily backfire and yield more disengagement.