The reason why you are not supposed to boil hot dogs is because boiling the hot dogs can impact the appearance, texture and taste of the hot dogs negatively.
Boiling the hot dogs also causes the fats in the hot dogs as well as the oils to cook out, which results in a less flavorful hot dog as well as a potentially dry hot dog.
Boiling of the hot dogs can also cause the hot dogs to become waterlogged and impact the texture and taste of the hot dog further.
There's no harm in boiling the hot dogs when it comes to your health and I've eaten boiled hot dogs a lot and still like them.
I prefer to grill the hot dogs but boiling the hot dogs is also okay.
Hot dogs are already cooked and ready to eat as is but many people prefer to heat them or cook them further by grilling them or boiling.
Some people also like to roast the hot dogs over a fire which is also okay.
Boiled hot dogs are just not as good tasting as grilled or roasted or pan fried hot dogs but they are okay to eat when boiled.
If boiling the hot dogs, just be sure to not boil the hot dogs too long or they lose more of their flavor.
Usually boiling the hot dogs for 2 to 3 minutes is good enough to heat them up.