Can usage of free software be restricted?

[Eric Feliksik]

http://www.ubuntulinux.org/legal reads:
<quote>
Use of Ubuntu software

Your use of any software obtained from this site is subject to the terms 
of any license agreement provided with the software. Some of these 
agreements incorporate the terms of the GPL or other open source 
licences. Please read these agreements before installing and using the 
software; by installing and using the software, you will have accepted 
the terms of the agreements.
</quote>

I don't like this. It's not realistic to read those licenses for normal 
use. Ubuntu ships software with many different licenses, and  reading 
the license of software like Microsoft Windows is a burden, but reading 
all of the open source license (GPL, MPL, LGPL, APL, X11-license, etc. 
etc. etc.) is a lot of work. (Yes, I know, after installing windows you 
install Nero, Acrobat, etc. etc. - and of course nobody reads it's 
licenses).

I really do understand copyright is copyright, and must be respected... 
So why do I complain?

Because I'm in doubt about the necessity of the instruction to read and 
accept the licenses. What free-software licenses do you have to agree on 
in order to use the software the license covers? AFAIK at least the GPL 
does not restrict usage in any way; this means the GPL has to be 
accepted *only* if someone wants to redistribute the software. If the 
GPL is not accepted, there is no permission to redistribute the 
copyrighted work. When installing firefox the license has to be agreed 
on, but does the Mozilla-tri-license require that? If not, does any 
other license do so? If so, what must be agreed on, if right 0 of a free 
software program is the freedom to run the program for any purpose?

Thanks, for your time. I can be wrong about some things, so let me know. 
I hope to hear your feedback.

Eric