It isn't necessary to take an extreme position one way or the other, and it just isn't warranted. Using tap water is like not having health insurance. It is a risk. Often it works out, and folks can then claim it was a good idea. Sometimes it doesn't, and then choosing that path might look foolish.
Tap water clearly does sometimes contain things that are unacceptable (high copper from pipes, for example). Sometimes it does not. A TDS measurement is no indication of suitability with respect to copper, since even totally pure water run through copper pipes can become too high in copper.
I discuss tap water, and include real data from many city water supplies here:
Tap Water in Reef Aquaria
http://www.advancedaquarist.com/issues/jan2004/chem.htm