ReveredChaplainDrake, the lascannon is much better than the missile launcher in Tactical Squads I'm afraid. The frag missile and 5 points you save are not worth what you lose (a point of strength and AP). This is really a no-brainer when it comes to points-efficiency.
The missile launcher outdoes the lascannon for cost in Devastator Squads on the other hand, but in Tactical Squads the viable heavy weapons options come down to the heavy bolter and lascannon.
The lascannon is just very efficient for it's price in a Tactical Squad (especially combined with a plasma gun), whilst the heavy bolter is cheap and effective at it's role (rather than poor at it's role as with the frag missile).
I think a plasma gun is the best option for a squad with true grit and counter assault. If you rapid fire the plasma gun and bolters at close range you won't be able to charge. But you'll get the benefits of an extra attack and moving your models in anyway due to the special rules (assuming you get charged).