2000BC: Here, eat this root
1000AD: That root is heathen! Here, say this prayer.
1865AD: That prayer is superstition! Here, drink this potion.
1935AD: That potion is snake oil! Here, swallow this pill.
1975AD: That pill is ineffective! Here, take this antibiotic.
2000AD: That antibiotic is poison! Here, eat this root.