That is not correct. You can search for documents, images, etc which all are not illegal. There are also many free programs and games available via P2P. Saying that Limewire is illegal just because you CAN, with your own choice, search and download illegal files does not make Limewire illegal.
It would be saying driving a car is illegal because you can drive over the speed limit, drive to rob a bank, etc.
EDIT: Just to add an example to prove Limewire is not illegal. I am part of a stock trading group and we run programs each night that produce raw data. That data is stored on a guy's computer/server and we all download the data each night or whenever we want. There is nothing illegal about that.
Limewire is not illegal and there are MANY people who use it for file sharing that have nothing to do with music or program stealing.