The Internet is just like "real life" -- just like going places, talking to people, etc.
You have to be prudent which neighborhoods you explore, and what kind of people you want to talk to. If you go up to a group of teenagers with nose-rings, you put yourself at risk to hear improper speech.
At any rate, there are no swear words on this site, and I have no idea what words/phrases the filter has a problem with.
I don't even own filtering software. I don't think that's a sin or imperfection on my part. When you use the Net, you have to be prudent, end of story.
Why don't I have a filter? Well, for starters, I'm a computer programmer and so I know what's possible and what isn't. A program can never have "reason" like a human being -- because only an immortal soul grants the spiritual faculty of reason. Therefore, a "net blocking filter" will be shotty at best. It will complain about a news headline "Sixth graders have sex during class." but might miss more important things.
For instance, when I studied Japanese, I often got my sentences filtered by various web forums. Why? Because there are 2 common endings, "-s h i t a" (past tense) and "-s h i t e" (present tense). The stupid program thought I was swearing! hahaha
When someone borrows your computer, it's like borrowing your car. You lend them your car, but NOT so that they can see (accidentally or otherwise) nude women on the magazines at the checkout counter. You lent them your car so they could buy groceries. It's the same thing. I don't think there is any moral guilt there (lending someone your computer without a "filter")
Slapping a filter on your computer and saying "I'm good to go, I have nothing to worry about." is like the whole "V-chip" thing they were talking about putting in TVs about 10 years ago. I don't think that would solve the problem of TV.
With Internet OR TV, a lot of prudence/supervision/prayer/carefulness is required. TV is easier since it's completely useless -- but the Internet is needed for many things. So we just have to be very careful where we go. One good pointer is not to just surf around in idleness, and "explore". Avoiding areas populated by worldly (irreligious) people would also help.
Matthew