It's intended to be used for security testing against one's own machines, demonstrating a vulnerability if it exists by directly exploiting it. The general nature of such tools, however, is that they can be used for good or for evil. It's just assumed that the bad guys have something of the sort already.
You know, when I look at what it is and what it does... I'm not sure I believe that's what it's 'intended' for, although that certainly is what they say it's intended for.
But anyway, in the end, it doesn't matter, it exists. Authorial intent is so 20th century.
Think of it like this. The exploits are already out there, whether they're public or not. MSF takes these exploits, and packages them into a coordinated tool. Sounds evil, right? A script kiddie can grab this tool, update it so it has the latest exploits, and voila! pwn the internet.
Well, they can do that without MSF. It's just harder.
Where MSF helps is with pentesters and other security professionals. When they perform a pentest or audit, tools like MSF/SET/Nexpose allow them to rapidly and accurately determine if a network or system is vulnerable, and prove it (within the bounds of the engagement's scope). Without these tools, a pentest would require far more tedious work.
That's exactly what it's intended for, actually. It was built by pentesters to perform their work. I'd rather my security tools be open sourced and available for all the world to see and contribute to. Doing so also compels lazy vendors to patch awful vulnerabilities.
Say you're doing a pentest, and your target has an IDS/IPS to both prevent infiltration and exfiltration of data. And while you discover a system that is vulnerable, the payload that you want to deploy to this vulnerable system would normally trigger an alert by an IDS. With some of the tools in MSF and BackTrack, you can use an encoding process to obfuscate the payload enough to get past the IDS/IPS.
Now a blackhat would be able to do this without BT or Metasploit. The tools are out there, and well known. So the fact that these tools are in BT and Metasploit doesn't change that. But it does make it easier for a pentester to prove a system is vulnerable, and to help a company address their vulnerabilities through remediation.
