Nope that's what you're supposed to do that way if someone isn't paying attention behind you to stop, you may have a chance to get out of the way. Also it's easier to get the bike to 1st coming to a stop than from neutral to 1st while not moving.
Nope, when the lever is fully pulled in the clutch is 100% disengaged, it's basically the same thing as neutral because no power is being delivered to the wheel. The lever won't be harmed, this is exactly how it's meant to be ridden . The good thing about bike clutches is they're MADE to be slipped unlike a car, so they'll last a very long time even when slipping (not that I'm suggesting you are sitting at a light, you're not).
You DO make a good pointIt's not safer... Good luck getting your bike into 1st when an idiot behind you won't stop... You SHOULD be holding in the clutch at a light (I wouldn't if I'm in bumper to bumper not really moving, but otherwise I have the lever in). Really it's all personal preference, but I'd rather be able to get the **** out of the way of a car than not be able to hold the clutch lever down for a minute.