You can. Create a standard wlan with no encription, enable full client isolation and put them on a separated VLAN that only goes out to the internet.
One thing to keep in mind, in an Open network any client that happens to be near by will associate and pull an IP address, if you do not have enough IP address and or your least time is not short you will run out of IP. If on the other hand you make your IP least time too short the client will go through DHCP renewal more often then is necessary good for the network.
There may be a few other concerns such as security (over the air packets are not encrypted)/privacy, illegal usage and so on, that other network administrator might be able point out as well. The configuration is easily accomplished, but please be aware of possible issues with such an open network.
