This may be another example where someone's "perfect" solution will be used against a good solution like VASIMR. Instead of working to achieve something practical in a reasonable timeframe, people are being lured by the hope of something "better" even though the technology is a long way from reality.

As Tom pointed out, we have no way to produce a controlled fusion reaction on the ground yet. I've been reading about fusion being "30 years away" for at least 30 years now. It seems the timeline just keeps slipping to the right. Until we can develop practical and efficient fusion reactors on the ground, I see little chance of building one for space use where mass is a critical factor.

As you pointed out, it'd take an enormous amount of energy to make a trip to Mars in a day or two. The biggest nuclear powerplants that I know about are all less than 1 gigawatt. 5 terrawatts is over 5,000 times the output of the biggest nuclear (fission) powerplants. It'll be a while before we can generate that kind of energy even on the ground where weight isn't a factor.