Helper classes considered bad OO

Too often developers put logic in so-called Helper classes. This practice of SPOD (Single Point of Definition) results in a higher level of reusability, so it seems. But in fact introducing these procedural structured behavioral methods impose a rigid structure. First of all, (other) developers need to be aware that such Helpers exist to work on their objects. Secondly, because behavior that should have been defined in the class of the object, is now defined elsewhere.