It appears to be an emotive subject, and as with most issues there's more than one side to it, each being valid in their own right.
Yes, it costs money to provide this free service, and it is very possible that it cannot be provided FOC any longer. But equally, there have been many announcements and a fair amount of noise from the management that it is a "free database, and always will be". Is this only the case until such as time as there was the opportunity to make large sums of money from it? Are there no alternatives to finance the required outlay to keep it running?
Equally, in regard to "free" services, it is reasonable to assume that members are willing to put their time and effort into improving the accuracy and quality of a free service for nothing because all would benefit from it. If this is no longer to be the case, are such members as likely to be as "charitable" with their support for it? For a service that appears to rely heavily upon the support of its member group, this is potentially crippling.
Ultimately, I'm not trying to argue for or against the charges; whilst I would like it to remain free, it is not my decision. My point is this:
What seems to be the most damaging is that the announcement to begin charging appears to be distinctly half-baked.
By all means, make an announcement that you intend to charge, and give an idea of the costs you are to expect, but also provide information regarding the likely questions of consumer support, concessions for contributions etc etc. Provide your future customers with as much information as you can, as not knowing breeds rumours, speculation and ill-feeling.
And if you can't work out what information you're likely to be asked for, then maybe you shouldn't bother with it at all. Even as a rookie uni student, I'd have been strung up for presenting a business plan like that!