You should try to avoid subverting a framework's conventions if you're going to use it, sure, but Rails' helpers seem more like an absence of convention. They're a dumping ground for methods that are crying out to be properly structured. Surely not even the most fervent Rails advocate would claim that it is complete and unimprovable.

Every single helper module is mixed in to every single view instance, no matter how irrelevant it may be. There's therefore no reason to carefully choose where to put your helper functions, because they're all available, all the time. This means that a new coder coming along has no idea where to look for helper functions that might be relevant to a particular view he's creating - they could be in literally any helper, or even be helper-ified controller methods. This in turn means you end up with duplicated functionality, orphaned functions, and obsolete cruft stinking up the joint.

As a result, any even slightly professional team must develop their own conventions regarding the placement of helper functions. These conventions need to be communicated somehow, and how better to do that than through the code itself? Once you've got a pile of helper functions that are bound by a common cause, why not give that cause a name?