I worried about that when I wrote the title. I thought about doing it this way:

A soft fork is a 51% attack (that we like)

But I took off the parenthetical because I wanted to emphasize the point that a soft fork only works if miners work together to reorg out miners who don't do it.

I also don't like the feeling I get that we have all agreed that soft forks are somehow okay and not risky. Hard forks sound scary and Bitcoiners generally view the idea of a hard fork with skepticism. Soft forks on the other hand, we talk about like it's no big deal. This is not the case.