Leaving the generate option gives new users the impression that they can easily make money, when in reality it's running their CPU at 100% and they will most likely never see a block created.
In my opinion is just a matter of comunication: just clarify that this options is not likely to generate coins but will help secure the network, and leave the people the choice on how to employ his idle cpu time.
Also, in the very near future energy will be almost free, just dig the news about Rossi's "e-cat
" on google, already validated by 2 universities (Italy and Sweden) and in commerce at the end of the year.
Anyway, if I'm understanding the thing right, even with very low hashing power, having millions of users could help secure the network and distributing more evenly the power of the pools.
Of course this could be done much better if the installer of the client had a simple option to download and run a hashing program using the GPU, but until this procedure is not made simple for the end user I think that the option to enable generation should be given, just renamed and better explained.