Agree. Nitrates used to be thought of as the "safe" part of the nitrification cycle (ammonia and nitrite being very toxic at any level above zero) and in older works one can find suggestions that anything up to 40 ppm is fine, some even suggesting certain fish will be "OK" much higher. But this thinking has been proven erroneous.
Scientific tests/studies on nitrate are still few when it comes to aquarium fish, but those from other fish (fish farms, hatcheries, etc) are now showing that fish are affected by any level of nitrate. The species does seem to be a factor, at least in the commercial fish tests, along with the level of nitrate and the length of exposure to that level.
When it comes to aquarium fish, we must keep in mind that with a couple of exceptions, none of the fish we maintain occur in natural waters with nitrates above zero, and those that do test are not above 1 ppm. So this tells us that our fish are never exposed to nitrate, just as they are never exposed to ammonia or nitrite naturally. It makes sense that if ammonia and nitrite are toxic, so too is nitrate. If fish have evolved to live in water free of all three--and we certainly know what happens when they are exposed to the first two and to increasing nitrate--then it makes sense to maintain them in water as low in nitrates as possible. The few studies that have been done clearly show that some species have difficulty leading to death with very low levels.
Dr. Neal Monks frequently writes that aquarium fish should not be exposed to nitrates above 20 ppm, and preferably not above 10 ppm, and keeping them even lower is wise. It is now known that all species of cichlids appear to have issues at 20 ppm, and nitrates is now being considered the first cause of Malawi Bloat, not the diet, by many cichlid experts.
My tanks all run < 5 ppm nitrate, and they are heavily planted, and I change 50% of the water every week. This is a very good habit to get into.