What Sci-Fi clichés do you resent?

[GTOM]

Not sure that logic holds. A generation ship is essentially a small island ecosystem that has to carry with it a steady state industrial economy and population of sufficient size to supply a labour force to maintain that economy and maintain the health of the ecosystem. That's not going to be small, we're talking tens to hundreds of millions of tonnes if not billions. If you have the technology and energy to send such an island on a journey to another star at at even a tenth of a percentage of light speed then the same investment of energy could launch a significantly smaller mass at a significantly higher velocity.

It isn't only overall energy that counts.
I did some calculations, if they are correct, at least they help someone intends to write a not so far future story i think.
How can a rocket achieve 1000 km/s? If it is mass is about 10 ton, and it has a GW reactor, it still leaves Pluto sooner than achieve that speed.
(Rocket equations with 1000 km/s exhaust could grant 0,2 m/s2 acceleration. But efficiency isn't 100%, fuel mass, cooling issues, so it is good to have 0,1 m/s2. Now calculate acceleration path.)
If they want to build a coilgun to boost it... with a million g acceleration, the length of the cannon should be still more than 50km.

A generation ship can have years to achieve such velocity.