I'm a firm believer in talent dilution being a huge problem, so if this is the standard that you set for full time hires then keep it. Although it may be a good idea to think about wether or not this problem is representative of someones abilities to fill the position. You don't want to fall into the trap of asking an interview question (albeit a fairly easy on in my opinion) that may not tell you how good someone would be at filling the postion your hiring for.
