You can easily replace cashews with blanched almonds for any recipe that calls for cashews. I have done this many times, especially with the cashew cheeses, dips, and creams. I have an intolerance to cashews. I wouldn't call it a poison, but it is a common food people are allergic too. There are many foods that cause allergies or intolerances in some people...cashews, pistachios, peanuts, gluten, soy, milk (whether due to casein or lactose), eggs, shellfish, yeast. That doesn't make any of these foods "bad" or poisonous for the rest of us (though some of the foods on that list I would argue are quite unhealthy and unnecessary in the diet and harmful and cruel to produce).

I think cashews are the "nut" of choice in vegetarian recipes because they are bland and softer than other nuts and easy to work with due to no shell? They make a good replacement for tofu for people with soy allergies/intolerances. You can use them to make a soy free egg free mayonnaise (almonds work just as well for this) that is similar to the tofu based one, or to make creams (including a vegan cream cheese), whipped toppings, and pie bases. With relatively few ingredients they are easily transformed into rich food that mimics dairy based foods. The texture and fat content along with blandness probably plays a role in the success of them in accomplishing this. But if you play around you can find other ingredients that work. Sunflower seeds or pumpkin seeds can also work in some of the dishes that call for cashews. Even white beans work in some of them.