Why should we conserve heritage sites?

Because it's a three dimensional tactile record of our past. Photos are nice documentation but you don't get the same impact on your senses as walking through a doorway or up a stairway where someone famous or ordinary walked decades (or centuries) before. Sometimes you get to smell the past which I think is neat... like the old fireplace or maybe the old furniture or linens/clothes... whatever. Heritage sites are a time capsule of sorts where you can see how our predecessors lived (or died)... and if we are lucky the same surrounding areas or environment is preserved. We can see how physically small they were too. Personally I think it's important to keep these sites even if it's only to educate... the experience of going through a place rounds out history lessons quite perfectly. History is valid to know otherwise we are doomed to repeat the stupid things and not learn from them. Just my opinion.