If you want me to take the claim that "a high protein diet is unhealthy" seriously, then you're going to have to provide something better than that article.
"Weight Gain" due to increased protein consumption is disputed[1]. In fact the premise itself can be disputed just by noting that weight gain can present itself in the form of muscle gain.
Bad breath: ...really?
Constipation: "This is because high-protein diets that restrict carbohydrates are typically low in fiber." I'm sorry, but why do high protein diets need to be low in fiber? That doesn't make any sense at all - any diet can be low in fiber if you don't eat fiber.
Diarrhea: Author provides no source.
Dehydration and Kidney damage: Both prevented by drinking enough water.
Increased cancer risk: The issue with these studies is that they don't provide necessary controls. Most people who eat red meat regularly are not doing HIIT, strength training, or going for walks. They are not eating their red meat on a bed of spinach. They are eating it between two buns and with a side of steamy fries (which are known to cause cancer[2]). If we look at the actual mechanisms for carcinogenicity, we find that eating veggies, not burning your food, and not eating cured meats, are probably as likely to keep you cancer free than switching your steak to a super whole-grain diet. Don't forget to also have a healthy gut, which prevents colon cancer[3]
Saturated Fat / Heart Disease / cholesterol: Again, no long term studies have had the right controls in place to conclude that Saturated fat, in the absence of unhealthy carbs/meats, are actually harmful. Only 20% of the cholesterol in our bodies actually comes from our food. Saturated vs nonsaturated is a debate being waged between actual RDs. It's not just "an effort to cloud an issue".
Calcium Loss: Actually, more Americans experience calcium loss as a result of NOT getting enough protein.
"Despite a widely held belief that high-protein diets (especially diets high in animal protein) result in bone resorption and increased urinary calcium, higher protein diets are actually associated with greater bone mass and fewer fractures when calcium intake is adequate. Perhaps more concern should be focused on increasing the intake of alkalinizing fruits and vegetables rather than reducing protein sources." [4]
Whether high fat and protein vs high carb low fat is "better", is going to remain debated until the end of time, because studies repeatedly show discrepancies.
The fact is humans from different geographies have evolved over time to accommodate different diets. This is why we see things like lactose intolerance concentrated in some regions but devoid in others [5]. Imagine ALL of the other mechanisms for body health and how they have evolved over time in different regions, and consider how silly it is to attempt to expose those which are harmful using broad studies with poor controls over only certain populations - while ignoring the underlying mechanisms for the actual harm.
[1]https://jissn.biomedcentral.com/articles/10.1186/s12970-016-...
[2]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4780226/
[3]https://www.ncbi.nlm.nih.gov/pubmed/26286349
[4]https://academic.oup.com/ajcn/article/87/5/1567S/4650438
[5]https://www.foodbeast.com/news/map-of-milk-consumption-lacto...