Yep, you sure can. However, using public (and non-secure) WiFi opens your computer to all sorts of nasty security vulnerabilities from potential hackers. You risk things such as malware infections, ransomware attacks, privacy and data loss, even identity theft. Using Fetch instead of public WiFi and non-secure WiFi is arguably the most secure way to connect your computers to the Internet.
In fact, while your computer is connected to public and/or non-secure WiFi, your computer can be compromised by hackers who are connected to the same network. So think about coffee shops, restaurants, diners, hotels and other places that offer public WiFi. The safest alternative is simply to download and use Fetch.