Tell us specifically the dangers to family and lifestyle that are commonly associated with each of the things on this list.
eating dessert - consumption of excess calories which can lead to obesity if one gets addicted to the sugar rush. FYI, lots of people are addicted to sugar in the U.S., and desserts are not necessary at all.
Thanksgiving feasts - a feast is a celebration where a group of people indulge themselves in larger quantities of food than are needed for sustenance. These feasts can lead to a pattern of overeating in the long term, as well as cause people to get very sleepy while driving home from the massive sugar crash while the body tries to regulate blood sugar after the bulk of the simple calories are consumed. Feasts are not necessary.
driving a motorcycle - driving a motorcycle is inherently dangerous because the bike only has stability when in motion under certain circumstances. Many, many people are seriously injured or killed riding motorcycles each year. Motorcycles are not necessary.
swimming at the beach - swimming at the beach has more inherent dangers than swimming in a public pool or not swimming at all. In addition to the many dangers lurking in the water, the wave action and currents can move people out to sea or down the coast with little warning. (I grew up swimming on the Texas beach in the Gulf of Mexico and can tell you from personal experience that this happens all the time. If you're not careful, you can get pulled out too far to swim back and drown from exhaustion. I had a few close calls as a teenager. And if you've even gotten tangled up with a Portuguese Man-of-War, you know that there are all kinds of dangers in the water. Lots of people drown in the ocean every year. It is not necessary.
mountain climbing (think scaling the side of a mountain) - This is inherently dangerous due to the heights and skills required. It is not necessary.
potlucks at church - see the notes on Thanksgiving above
hunting - I have known people who have been shot or killed while hunting. You can buy meat at the grocery store. It is not necessary.
skiing - I've known a lot of people who have been injured skiing or snowboarding... One friend even broke his spine and spent months in the hospital. It is not necessary.