It depends on the context.
There is organised doping (think festina, t mobile astana maybe) so in these cases, if it can be proved, yep chuck them out.
There's also indvidiuals doping like that fellow from cofidis the other year, i wouldn't think for a minute that his frenchie teammates were on the fiddle so on them, it;s ufair.
Lance reckons that there was no doping, yet, quite a few of his teammates over the years have subsequently returned positive tests. even the most anti lance fan would find it hard to prove, or argue, that it was organised doping within his team. in this context it would be hard to disqualify a man who has no control over the preparation of his teammates.