Normally I would say it is a bad idea to totally bas one's argument off an assumption, and I think that that is usually a good rule of thumb to follow when constructing an argument, especially if there can be found a whole in your argument based on the assumption that you made right from the start!
However, in this instance I feel that her assumption if somewhat justified. The writer attempts to back up their argument by tossing around names of other people who believe as she does, and instead of trying to argue against them she decides to assume they are correct and argue with them. It is an interesting stylistic way to present an argument.
It does solve the problem of having to argue that point, as she comes off right from the bat stating that she will not argue that and that the whole argument is based off the idea that is taken for an assumption. And while I originally thought it would be ineffective and not work well in the thought process of an argument, it ends up working out quite well for the writer throughout the course of the article.
It works for one reason, and it is because of this that I think it is justified to use that assumption. I can find no holes in that assumption, and it is a very fit and sound one to start off an argument.
For is the whole abort