Filters are good so you don’t accidentally come across something you don’t want to. Google can be a problem with this as mentioned. safe search can eliminate some of these problems.
Many people can get around filters if they really want to. But it is still a deterrent. The more steps you have to take to get there the more chance that your yetzer tov will step in at some point in the process and stop you. Everyone has the Pintele Yid in them telling them to do the right thing.