When outside in the hot sun, you sweat. Do you cool off faster by standing in the shade with no breeze, by standing in the sun with a breeze, or standing in the shade with no breeze?
Obviously, in the shade with a breeze. Now imagine lack of breeze=weapons fire (massive heat-producing activities), sun=other systems that cause heat buildup.
+Sun -breeze = firing lasers and such
+Sun +breeze = combat maneuvering, EW, reactors up to combat levels, etc
-Sun +breeze = combat systems off and reactors turned down
Think about the difference between standing in the shade with and without a breeze. When in the shade, you're cooled by radiating heat (black body radiation) and the wind (convection). The breeze is cooling you off a lot more than merely radiating the heat is.
How hot would you be if there was no wind, ever? Add lasers and fusion reactors and computers and any other system that generates heat as a byproduct. Tell me you're not begging for that wind.

Now, add armor. You have to armor spaceships with guns on them, else the first enemy spaceship with guns on it that comes along pops you in a few shots. Look at construction cruisers and freighters.
What about armor? Unless you can design armor that only transmits heat one way (which could very well be possible), then any heat generated by weapon impacts will be transmitted to internal systems. This is bad.
Heat dissipation in space is a problem. Convection is an excellent method of heat transfer, but by definition it's one that's not available in a vacuum.
Solutions (viable or not)? Get enough surface area to radiate the heat efficiently. Convert it to electricity. Have massive internal reservoirs. Make your systems not produce any heat.