You also get another pick thingy, a little soft case (easier to pocket than the chunky hard case), another standard socket adapter, and a 1/8th-to-1/8th volume attenuator. If you plug the earphones in through the attenuator, it makes them quieter.

There's a good reason for the inclusion of these fixed and variable volume control devices. Without them, it's easy to damage your hearing with canalphones.
Is this part taken out of context? I don't get where it's coming from, unless its reasoning was in the content to follow.

There are two things that make earbuds and canalphones particularly dangerous.

One: Their maximum volume level is generally higher than that of full-sized headphones, mainly because big headphones, even sealed-back models, aren't as directly coupled to the eardrums. Even weedy portable player headphone amplifiers can drive most earbuds to alarmingly high volume levels, especially if the wearer doesn't care (or know...) about distortion.
When it's worded like that, then I'll have to agree with you (DS) that " they (canalphones) have the most potential of destroying your hearing."

When "potential" is read as the "physical ability" or "power" to induce hearing loss, then yes, I agree with your previous statement. Canalphones/earbuds have smaller drivers, which in turn means they use less power, an mp3 player with X amount of power can drive the volume higher when using canalphones/earbuds than large headphones.

However, my original interpretation of "potential" was "likelihood". Canalphones have a degree of noise isolation while open circumaural and regular earphones don't, so they need less volume to drown out ambient noise. A person headphones without noise isolation would need to turn it up louder to obtain the same SNR. When you use SNR as a control, open-earphones would be more likely to lead to hearing loss.

Canalphones would only have more "potential" (in the ability sense) because they are physically capable of being louder, but this argument requires the assumption that users will turn it (volume) up because they can, which isn't necessarily valid when talking about the "dangers" or "risk" of hearing loss from using various types of head/earphones, which I take as the underlying point of our discussion.

In the end though, this comes down who which interpretation of "potential" we are talking about. Potential = ability (and what I assume was your take on the word), by dictionary definition solely, is more correct.

Two: People usually wear these tiny headphones in noisy environments, so they turn 'em up to cut through the sound of the train or city street or whatever. Earbuds are far worse in this department, because they don't seal the ear canals and thus let in lots of outside noise.
I don't consider this a point at all against portable earphones. Interestingly, this point utlises the "likeihood" definition rather than "ability".