no P2P just arent spyware/malware or virus in itself. agreed KAZAA is a culprit.
but LIMEWIRE, SHAREAZA, WAREZ, EMULE, arent a problem.
P2P allows you to download files from someone else computer... so if you download files such as .exe, .com, .rar or .zip and others, you need to first scan it for virus... cause the data cant be reliable.
.
pictures, music and movies can be downloaded without any hassels.
.
maybe the p2p you have, had already been infected by a virus. download the software from a reliable source.
.
P2P doesnt slow the computer either... only that they eat your internet bandwidth (depending on your usage of the P2P).
they may slow the computer when your're sharing many files... so when the p2p starts, it needs to either index the file or make it ready to share with other peers... this will happen only when the p2p initializes so chill out till its done.