It is certainly a matter of personal preference, and if you put a weapon-mounted light on a handgun, you should understand how to use it without violating Rule 2 about not pointing a gun at anything yo are not willing to destroy. This is why you should use one of the high lumen lights such as those from Olight, SureFire, Streamlight, etc. They can be used very effectively to identify a potential target WITHOUT pointing the gun at the subject, should it indeed turn out to be a friendly such as one of children/grandchildren. The illumination area from these high output lights will "splash" enough light to positively I.D. a person without shining it directly into their face or body.
The point about the hot gasses from the front of the cylinder certainly makes sense, and if you choose to use a handheld light instead, make sure you keep your hand behind the front of the cylinder as well! The Harries Technique, Rogers/SureFire Technique, or Neck Index Technique will all keep your support hand safely behind the front of the cylinder if you do them correctly.
S&W made the M&P R8 .357 that came from the factory with a bottom and top rail; it looks pretty cool, but I've never used one. Perhaps someone who has used one could offer some insight?
One argument for using a WML is that it frees the support hand for other tasks such as mag changes, leading a loved one out of harm's way, calling 911, opening a door, etc. Many folks use both a WML and a hand held light effectively; either way you should train/practice (unloaded gun) to become proficient with your chosen method.
To each his own!
