Show me studies that say creatine causes kidney problems. Stomach problems like diarrhoea are small stuff, nothing to worry about. Most side effects from creatine are there because people don't drink enough while they are on it anyways.
The lists the following precautions when taking creatine.
Precautions of Creatine
Because of the potential for side effects and interactions with medications, dietary supplements should be taken only under the supervision of a knowledgeable healthcare provider.
Side effects of creatine include weight gain, muscle cramps, muscle strains and pulls, stomach upset, diarrhea, dizziness, high blood pressure, liver dysfunction, and kidney damage. The weight gain is thought to be due primarily to water retention. Creatine should not be used by anyone who already has problems kidney function, high blood pressure, or liver disease. Taking creatine supplements may prevent the body from making it's own natural stores. The long-term consequences of this are not known.
A 2001 report by the Food Safety Agency of France (AFSSA) raised questions about creatine supplements possibly putting users at greater risk for cancer, particularly if such supplements are taken for long periods of time. However, the European Commission and the Council for Responsible Nutrition in the United States both determined that AFSSA's claims are unsubstantiated and not based on any scientific evidence of a connection between creatine and cancer. All three organizations do agree, though, that risks of long-term use of creatine are not known at this time.
Creatine supplements containing contaminants from the production process have been reported. Be sure to buy products made by established companies with good reputations, and who distribute their products through trustworthy and knowledgeable establishments.
I'm actually surprised creatine is not banned somewhere in the world as other products have been banned without such evidence.