Most tree nuts are a good addition to include in a healthy diet, and it has been shown that those who regularly consume tree nuts live healthier, longer lives. There are many different kinds of nuts, some people think peanuts should be included although technically they are not a nut but a legume.
While macadamia nuts may be high fat they are not the unhealthiest. I would say the only real unhealthy nut are those that have been ‘honey-roasted’ because of the inclusion of sugar in that process. Similarly most salted nut varieties tend to contain excess sodium which can be a health consideration for those on low sodium diets.
The only nut I have read warnings about are Brazil nuts and that is because they tend to be very high in selenium. Each Brazil nut tends to have between 68–91 micrograms of selenium and the safe upper limit for adults is 400mcg. Anything above that is considered a selenium overdose.