That is true.. Safety is paramount when you deal with large objects in space. Also if we can find to turn Jupiter into a star (like 2010) I think that can help Mars terraform a bit.
I think that if Jupiter were a good star candidate, it would have become one. On the other hand, Jupiter has a few large water-rich moons to play around with so it would be possible, for example, to hit Mars with Europa and still use Callisto and/or Ganymede if another hit is desired or to hit Venus. Sure, comets could be used to add water to Mars but one of those big moons would add a lot of water and, as a bonus, re-liquify the planet and get a magnetic field going again and possibly add a nice moon. The evidence strongly suggests the magnetic field is very important for life and if it’s rare to keep one for a few billion years like Earth has, that’s a real strike against the odds of extraterrestrial life and especially intelligent extraterrestrial life. The magnetic field keeps the solar and cosmic radiation out and also keeps the atmosphere from being whittled away by the solar wind.