I'm not opposed to rails generally, but I am opposed to rails being added to older guns and (in my opinion) spoiling the aesthetics - primary offenders in this category are the 1911, SIG/Sauers (especially the 220), and the Beretta 92 Vertec/M9A1 (but not the 90-two). Besides, many of these mandate a different holster which is a pain if you own the older version(s) or if the powers that be in holstermaking decide not to update your chosen model.
I'm not opposed to lights mounted on handguns for HD or Tactical duty with the understanding that the odds are extremely good that if you encounter some type of villain who happens to be armed with a firearm of his own, he's quite likely to fire at the light (which depending on your position may involve him firing directly into your center of mass) - this is a reason why Police officers still carry seperate duty lights (though the main reason still involves being able to employ a light without employing a gun) and are still trained to hold it over their shoulder for the most part. (Note that SWAT Officers decked out in full body armor don't share a lot of these concerns).
Anyway, back when I had my Springfield XD and it's accompanying Tac-Light, I kept it mounted for HD duty because it gave me more OPTIONS - my primary light was the Surefire 6P next to it, but in the event the 6P burnt out or was dropped or I found myself in a situation where I thought the benefits of having a light on my gun outweighed the risks, a second source of illumination was just a flick away. Options are always a good thing, and to say that I'm flat out opposed to rails or using rails just limits my options.
Rails have also found a new place in my heart ever since Lasermax saw fit to develop a trim laser unit that mounts on most handgun rails - which is a great way to get a laser on your HD handgun where a standard Lasermax or Crimson trace unit isn't feasible or available (it also allows you to move the laser from gun to gun, including long guns, as long as there is a compatible rail available - always a plus).