You are correct in theory, but there are so many conditions in your answer that you have really proven GP's point.
Even if you make sure that information gain about an individual from your dataset is minimal, this could easily change if combined with other data sets, as GP stated.
Saying we shouldn't use these techniques because it's hard to implement them correctly is like saying we shouldn't use cryptographic methods like RSA because they are hard to understand. You don't need to roll your own version of RSA to use it, and you don't need to implement your own k-anonymity/l-diversity/t-closeness implementation to anonymize your data (see e.g. [1] for an open-source tool to do this).
