Aren't you innocent until proven guilty? Simply saying "I have a guest network" surely constitutes reasonable doubt, in the absence of any other evidence against you.
So, theoretically one could ride the reasonable-doubt-train all the way to court but at that point, the prosecutor would stack any charge possible leaving the jury to deliberate on all them. Modern day juries still most likely are not computer savvy so, merely stating "IP Address" would most likely be enough to convict. It is also needs to be added that if the charges are severe enough, even though every defendant is innocent until proven guilty, in reality it is the opposite way around if the said crime is vehemently disliked by all.
You'd still face an average of 6 years of legal wrangling and attendant expenses.
- Leaving a window open, or a door unlocked, thereby allowing someone to enter through it, and while on your premise conducts a crime. Is this crime your fault for not sufficiently securing your home?
- Someone enters your yard because the gate wasn't locked and sells some pirated movies or drugs. Again, is it your fault because you didn't sufficiently secure your 6 foot fence from intruders?
Interestingly where I leave a major Canadian ISP provides unsecured wifi networks across the city. To get access all you need to do is register your ethernet address to your account. As we know it is trivial to spoof an ethernet address. So, I suppose this ISP could be liable as well? Oh, wait--they are just the pipe. So, why is the consumer treated different? Sigh.