I will tell you why. There are several action cams available. If you are a starter, you probably will buy yourself a rather inexpensive one. So did I. I bought myself a Sony camcorder. The picture was acceptable, but I was not able to see what I was filming. This is also the case in the more expensive GoPro action cams (like the GoPro Hero 5). There you only can see what you are filming if you are filming somebody else. If you go for a selfy, you need to guess how to hold the camera.
The next thing was that the action cams do not have that great audio. Perhaps in the most expensive ones the sound is OK, but still. What you want is a good video with great sound.
Then there is the fish eye. Due to the lens of the action cam, the picture gets distorded. If you want to remove the fish eye effect, you need to post-process the video on your computer.
Now why would you prefer an action cam over a regular camcorder?
1. The action cam is small and very portable. Most of the camcorders are big and can’t be placed on a selfy stick.
2. Some of the action cams are waterproof (remark: some of the camcorders also are waterproof)
3. Most of the action cams are resistant to some degree of shock
Why would you prefer a camcorder over an action cam?
1. Due to the bigger lens and (usually) bigger chip, the video quality is a lot better.
2. Very slight of no fish eye distortion
3. Better audio and (for some models) the possibility of attaching your external microphone.
4. For some models: being able to add additional lenses for effects.
5. Zooming. In action cams you can only do digital zoom (this basically is enlarging the existing footage). In most of the camcorders you have optical zoom. This does not damage the footage and keeps it crisp.
6. The vibrant colors. Some of the camcorders have spectacular livid colors. No post processing is needed.
So If you want to buy yourself a camcorder. What camcorder to use?
I bought myself a Sony FDR AX-33. This is a 4K camcorder (so huge film resolution). It has great video. Good mechanical image stabilization (the lens moves slowly when the camera is moving fast, to prevent shocks in the movie). It has a microphone output. You can connect it directly to the computer. It has the possibility to mount additional lenses (for example to film something that is very close to the camera or to get a more action cam like film. And most of all you actually can see what you are filming!
Most of all these camera’s can be bought second-hand. This made my camera just as affordable as an action cam.
If you want to go for even better video quality, you can go for a more expensive camera with a bigger chip.