When people speak of moral decline, it's usually focused on moral standards. Someone with 1950s moral standards would find what's acceptable in 2023 a huge moral decline. Someone with 1880s moral standards will probably have felt the same for 1930. And ancient romans would probably think 1880 too "square". This is not about specific criminal behavior (like the "have you been mugged"), but different moral concerns.
An 1950s or an old West person would find most of current acceptable moral standards adhorent for example (things like etiquette, attitudes to sex, how young people speak to their elders, going to church, dressing appropriately, abortion, how kids behave at school, what is allowed to be mass broadcast, etc), even if in their society violent murder was many times more prevalent, or they still had some practice we find bad today.