You "could" edit the toolbar configuration to leave out the view source tool button, however, the places where the editor has the view source button are only in places where the features expect trusted users. For example the blog comments and forums do no expect trusted users so they don't have as many toolbar options, but the Html content feature and the Blog feature do expect users with edit permissions to be trusted users. You should not allow untrusted users to edit those features. See the section of What mojoPortal is NOT designed for on the About page.
Hope that helps,