The point is that if you sandbox all untrusted/unknown programs, then they won't be able to harm your system should they end up to be malware. However, the important thing that it seems Melih (Comodo CEO) is oblivious to (since all he talks about is how the sandbox is so amazing on his forums), is that if malware is executed in a sandbox (no matter how powerful it is), it still gives it a shot - in terms of exploits, the sandbox can be exploited and lead to the system becoming compromised by the attacker. Attackers have found ways to compromise software such as VMWare Workstation before from the Guest OS, very sophisticated, also using real virtualisation techniques via hardware utilisation, therefore Comodo Sandbox can also be exploited (theoretically, nothing is 100% secure and everything can be exploited one way or another, even if it seems impossible at the start).
In reality, Anti-Virus software is not actually dead, since they still have a chance at detecting malicious software before it gets to actually execute (which would then give it at least a 1% chance of exploiting any security software techniques such as sandboxing). Even though detection methods such as checksum scanning is now obsolete and has been for quite some time, in my opinion at least, heuristics is a big thing when it comes to AV development and can always kick in and be helpful with positive detection's, too. Web-blocking is also a huge factor when it comes to security software, since you can block the downloads before the malware is ever downloaded onto the system in the first place, or before an exploit page has successfully finished with the web requests to the browser to load and execute the exploit.
If possible, prevent the threat from ever making its way onto your system. The best line of defense in reality is actually you, and additional security software or browser extensions are just your backup friend - watch what websites you visit, watch what you download and watch what you run. That being said, never trust an e-mail without verification of the sender should attachments be handled or links be involved (since attackers can spoof the sender email via altering the email header for example). Just apply good online practises, and be careful when handling things offline (such as removable disks), and you should be fine with or without any security such as Anti-Virus/Internet Security.
Comodo Sandbox is very good if used correctly, but it's not as good as some people make out, most security software is overrated since it's just people handing out opinions on which software they like - and this is natural and normal on a forum, all forums actually. Use the software you are comfortable with using, but just remember that no matter what you do, you're not 100% secure and malware/hacking techniques are evolving every single day, you never know what is around the corner waiting for you the next day!
