[quote=ASTA]
They wouldn't be terrible in space, since hard sci-fi military ships wouldn't be the lumbering armor-clad WWII-knock off vessels most sci-fi portrays them as. They'd be light, so as to conserve delta-v during maneuvers---and to make it easier to accelerate, decelerate and alter their trajectory--- which means they'd have less mass for a laser to burn through. A sufficiently-powerful laser would easily burn through a ship's hull, compromising it and potentially dooming the crew inside. As for the speed, the thought of effortlessly dodging laser fire with a slow-than-light vessel (that obeys the laws of physics) is pretty much inherent to soft sci-fi where antimatter weapons, warp drives and phasers are the norm, as any ship packing laser weapons is going to have them mounted in fully-traversable turrets. While a space warship may be able to dodge one laser, the other 30 that are taking shots at it create an absurdly-large arch of inter-locking fire that simply cannot be avoided. And not only that, but as space lacks an atmosphere, lasers become even more dangerous, as there is nothing in their immediate path (or surroundings) to degrade or scatter their beams.
[/quote]

*Shakes head*

A: No, a ship mounting lasers for ANYTHING except point defence is NOT going to mount them in fully traversable turrets. It's going to mount it as a spinal weapon where they can get the most surface-area for the laser (Necessary, as your laser gets more powerful the size of the laser PROJECTOR increases with it.)

B: Your laser will be good, at MOST optimistic for a single light-second range. (299'792.458km) beyond that you're going to be less accurate than missiles (which in turn are terrible due to vulnerability at that range where any missile could be shot down so easily they literally aren't worth launching.) And as Brovo pointed out, the laser diffusing over range

[quote]The good ship Collateral Damage becomes aware of an incoming hostile missile. Collateral Damage has a laser cannon with a ten meter radius mirror operating on a mid-infrared wavelength of 2700 nanometers (0.0000027 meters). The divergence angle is (1.22 * 0.0000027) / 10 = 0.00000033 radians or 0.000019 degrees.

The laser cannon has an aperture power of 20 megawatts, and the missile is at a range of four megameters (4,000,000 meters). The beam brightness at the missile is 20 / (π * (4,000,000 * tan(0.000019/2))2) = 15 MW/m2 or 1.5 kW/cm2.

If the missile has a "hardness" of 10 kilojoules/cm2, the laser will have to dwell on the same spot on the missile for 10/1.5 = 6.6 seconds in order to kill it.

Figured another way, at four megameters the laser will have a spot size of 0.66 meters in radius, which has an area of 1.36 square meters. The missile's skin has a hardness of 10 kilojoules/cm2 so 13,600 kilojoules will be required to burn a hole of 0.66 meters radius. 20 megawatts for 6.9 seconds is 13,600 kilojoules. 6.9 seconds is close enough for government work to 6.6 seconds.[/quote]

On THIS note...

[quote]And not only that, but as space lacks an atmosphere, lasers become even more dangerous, as there is nothing in their immediate path (or surroundings) to degrade or scatter their beams.[/quote]

Go back to school and learn how lasers REALLY work.