You are a grownup and will do what you will. You should, consider, though that people can -and have- been busted for illegal stuff done through their open WiFi without convincing evidence nailing said illegal conduct down to a particular person.
And as TDT pointed out earlier, if people see your computer equipment being wheeled away by the police malicious gossip is going to start. This will at best make for uncomfortable living for the (probable) months it'll take the police to process. There's a real chance of verbal and physical attacks against you and your family (if applicable).
Then there's proving your innocence. Proving you did something is relatively easy...you produce logs; paper trail; witnesses etc. that place you at a particular place at a certain time doing a certain thing. Proving you didn't do something is very much harder; especially if it's illegal behaviour (as opposed to a particular incident) like kiddieporn that could be done at any time over a period of months or years.
All this so far has been discussing someone using your network as a passthrough for their own illegal activities. Now let's discuss malicious:
1. It is trivial to set up a high-powered Wifi access point with the same name. Your machine will default to the best signal, so chances are you'll connect to the fake; probably without noticing. So the attacker monitors your (unencrypted) signals; and that will in fairly short order give them login to your email account and 2 hours after that probably the rest of your online personae/s.
2. Paranoid scenario. A neigbour (or frequent drive-by) user of your network actually is into kiddieporn. What better way of allaying suspicion than to inject a couple of KP folders into your system and providing the police someone to work on? Your kit is going to be easier to get at because it's sending everything in the clear and you leaving Wifi open strongly suggests that security is not one of your priorities. This can and does happen and has been mentioned in several spook agency notes as a fast and reliable way of discrediting people.
An open wifi network does not give you a get out of jail free card in relation to copyright infringement either.
Chances are nothing will happen (although the odds are shortening as time goes by). But if things do go wrong; the potential for them to go very badly life-fuckingly wrong is just not worth the risk when the solution is so simple.