there's a shitload of real data here:
http://www.netspeed.com.au/ttguy/refs2.htm
a dogmatic/religious angle:
http://www.porn-free.org/porn_is_bad.htm
my personally favorite quote is from the religious page:
"5) Pornography intensifies an individual's drive to serve oneself, rather than serve others."
and this:
"7) By viewing and purchasing porn, you are supporting the porn industry and facilitating its growth."