What are the dangers of riding a dirt bike shirtless?

I was ready to ride my dirtbike all geared up (pants, helmet, boots, etc.) besides a shirt. I have an 80cc honda and a pretty skilled driver. However my father came out and yelled for me to stop and made me put on a long sleeve shirt. Was this right to do? Should he have just let me ride or was he right?

Even with a long sleeve T-Shirt on, you're not protected good enough. The material will tear as soon as you hit the ground if you did fall from the bike at speed. It's still better than no shirt however. You should at-least get some kind of armour for your back and chest, in my opinion. One that you could strap over the top of your shirt. Even skilled riders don't ride without gear.

I know it sucks, but I wear tee shirt, upper body armor, then a jersey. I wear my race pants, plus boots. Yes I sweat. Omg do I. I wear a camel pack with ice water for that. Now I don't track ride, I CC and enduro. I change gloves during pit stops. Your probably to young for this, but riding in no tee is the best way to remove a tattoo or nipple.

Bees.
Hornets.
Yellow Jackets.
Branches.
Branches with thorns.
Sunburn.
Windburn.
Dirt ground into your arms, shoulders, chest, back, etc. When you fall.

Your father has to pay when you get yourself injured.
When you are 18, out on your own, paying for your own injuries, then you can ride shirtless.

If you ride more than 5mph and hard enough to put a smile on your face, wear proper gear. A good jacket or jersey and chest protector will save you a a lot of pain when you do crash. Even a small stick can do serious damage when you land on it (ever have a 1/2 inch stick tear through/go under your skin?). Ever land on a sharp rock and tear through tendon? Kiss your summer goodbye! Your dad was right.

You're young, the missing skin will grow back.
Might leave a scar or two but that doesn't matter unless you want a tattoo later in that spot.

Oh! You can't race that way in any sanctioned race org.

In my opinion, there's nothing wrong if you like to go shirtless. A long sleeve shirt would not protect you unless you go 100% with those protective gears such as leather jackets, etc… The only thing that it would protect is from the sunburn but you can always wear sun screen to protect your skin. Besides, there are always some risk with riding dirt bike so just use caution and Good Luck!