People will just say whatever they think their peers want to hear. What people say doesn't tell you what they think or do.
Definitely more than 50% of people watch porn, despite this. A significant % of 'homosexuality is immoral' types have grindr accounts. Many women who say abortions are wrong also say their case was special and unique which makes it okay. That using marijuana one would definitely be higher before it become widely legal. Gambling too would've had more disapproval before private gambling rings were allowed to advertise at sport games.
These stats reflect public policy, rather than guide it (to a large extent) is my point.