I actually have two wireless networks, the "public" one that I really don't care what happens on, and my private one that is restricted to my connections.
Just my $0.02 - you should care - you're responsible for any attacks that originate at your public ip address.
Many people feel that, because of the dynamic nature of things on the internet, that such attacks cannot be traced back to the source - this is incorrect and your ISP will have logs that show which subscriber had a given ip at a given time, even with dynamically assigned addresses.
I like to "illustrate" things, so if you'll just allow me ...
I live in a fairly small third world country where not every one has a computer in their home, and small "internet cafes", where you can buy a few hours of online time for a small fee are quite popular. DHCP addressing is the norm here, static address are available for a fee, and due to an unreliable power utility, the norm is to shut down everything and unplug, when you close business at the end of the day - I mention this so that you know the ip addresses change pretty much on a daily basis.
Someone used one of these cafes, located in a small town outside of the capital city, to send a threatning email to an airline, copying to the US state department - and even though neither state nor FBI has any jurisdiction here, within 24 hours of the email being received, the FBI, with support from the local police had raided the cafe, seized equipment and detained the owner & operator of the cafe to assist in the investigation.
The owner was released after a couple of days, and the equipment eventually returned, as there was no way to identify who actually sent the email - since no records of identity were kept at that time, legislation has since been past requiring cafe operators to keep such records.
Think about it - someone, parked outside your place, connects to your public WiFi and starts snooping around TSA or Homeland Security - or for that matter, someone, who knows where on the internet, takes control of a bot in your "DMZ" and does the same.
Where does the trace point to? Whose door are the Feds knocking on? Who are they going to detain "to assist in the investigation?