"If a person wants to install non free software, she finds lots of ways on
the internet to do so."
Exactly, so there's no need for the Debian Project to do so.
"I don't see any practicle difference if it is offered and documented by
debian instead of somebody else."
As you say, people can find information about how to install non-free
software on the Internet so there is no need for the Debian Project to also
do it. To quote from http://www.gnu.org/philosophy/compromise.html
"The issue here is not whether people should be able or allowed to install
nonfree software; a general-purpose system enables and allows users to do
whatever they wish. The issue is whether we guide users towards nonfree
software. What they do on their own is their responsibility; what we do for
them, and what we direct them towards, is ours. We must not direct the users
towards proprietary software as if it were a solution, because proprietary
software is the problem."
