Thor didn't accelerate its weapons, it just dropped them into a gravity well. No recoil due to taking advantage of potential energy.
I did not say it accelerate ... I say "kinetic power". If you use weapon against "land" targets kinetic round are superb. No warhead ect. just one big piece of metal. Laser are point weapon with no real kinetic power, good for delicate shoots but if you want to destroy something in good old way you use kinetic rounds.
Pushing the round forwards pushes the weapon backwards equally, even with a coil or rail gun. They impart force on each other thanks to Newton's third law.
Do you have any idea on what power level we talk ? Brits' 14 inch Mk VII naval gun accelerate bullet 750 m/s ... and thats a one big fraking gun. Railgun accelerate 3,500 m/s ... You think someting would hold in one place THAT! kind of weapon. One shoot would rip off whole gun from ship with large piece of that ship in opposite direction when they shoot.
Again, kinetic weapons generate much low recoil. There is no propeellent, bullet do not have physical contact with the barrel.
If there is like you say barnest2 ... railguns, coilguns whatever, would be totaly useless. And they are not.