You have to give -s as a start parameter to Rebol.
>> usage
The command line usage is:
REBOL <options> <script> <arguments>
All fields are optional. Supported options are:
--cgi (-c) Check for CGI input
--do expr Evaluate expression
--link url Connect to Link
--help (-?) Display this usage information
--nowindow (-w) Do not open a window
--noinstall (-i) Do not install (Link, View)
--quiet (-q) Don't print banners
--reinstall (+i) Force an install (Link, View)
--script file Explicitly specify script
--secure level Set security: allow ask throw quit
--trace (-t) Enable trace mode
--uninstall (-u) Uninstall REBOL (Link, View)
--version tuple Minimum version of script, when URL (View)
--noviewtop (-v) Do not start viewtop (view desktop)
Special command line options:
+q Force not quiet (Link, View)
-s No security
+s Full security
-- args Provide args without a script
Examples:
REBOL script.r
REBOL -s script.r
REBOL script.r 10:30 test@domain.dom
REBOL --do "verbose: true" script.r
REBOL -cswq
REBOL --cgi --secure throw --script cgi.r "debug: true"
REBOL --version 1.2.3 http://www.rebol.net/test.r ; view only
Although usage shows the same in R3, I guess security is not or not fully functional in Rebol3. Also some of the most recent versions of Rebol2 have a slightly different behavior regarding -i or --noinstall.