Why does my opinion of other women upset my girlfriend?

We were watching tv the other day and she asked if i thought pam anderson was hot, i said yes, she was like- ‘really? she’s so trashy!’ i explained that i would never sleep with her or anything but yes to the eye she is physically attractive. She explained she understands the fact that i will find other women attractive, but she hopes that i will have standards. I feel the need to say something like ‘i’m a guy i can’t help the way i’m programmed, i can’t help it that large breasts and pretty faces are appealing to me’ but i fear this would be more upsetting. How can i explain this to her?