Kind bars have 18% saturated fat. Should they be avoided by people with high cholesterol?

No. The 18% you are referring to is 18% of what is suggested for a normal healthy diet in one day. The saturated fat in Kind bars comes mostly from nuts and is a healthy form of fat. Also not all Kind bars have the same amount of fat. For example the fruit and nut delight bars have 1.5 grams of saturated fat which is only 8% of the suggested daily amount of saturated fat.
Fats. Although fats should be monitored, it is likely excess carbs that do the damage. Look into a low glycemic diet.
Saturated Fats. Saturated fat, derived chiefly from animal products, raises the total serum cholesterol. To answer your question, yes it may increase your cholesterol levels.