First off, I hope we can do away with the euphemisms in this discussion. "Free", as normally used in these discussion equals "available for anyone anywhere for for-profit purposes".
So call it libre---others have. In any case to say it is "equal" to "available for anyone anywhere for for-profit purposes" is a blatant distortion: "free" means not the ability of users to make money but the inability of distributors to restrict their customers' freedom to use, modify and share the product the distributor provides.
The
option to make commercial use is a distinctly positive thing. Suppose we moved CZ to a non-commercial-only license, and someone wanted a hard copy of some of the material. They can't pay someone to do this for them because that person then becomes a commercial distributor (not allowed), so they have to either do it themselves (they may not have the skills or equipment or even the access to the material in the first place), or rely on someone else's charity.
Or suppose someone wanted to create a copy of Citizendium in another language, open to all on the web in the same way. Perhaps they want this to happen fast: one way to hurry this along would be to pay people to do translations (governments are already doing this with free software and its documentation), but again, the translator technically becomes a commercial distributor as they are being paid for a derivative work of the original, so it's disallowed.
I do not like idea of making money on my work that I do for free in the aim of sharing my knowledge (otherwise, I'm used to get paid precisely for that). I prefer the two aims, sharing and profiting, to be separated, at least theoretically.
I think it depends on the scale on which you think. If it's on the scale of individual articles, then obviously you might feel reluctant. One difference with free software is that whereas once the software is written you will use it (so you have a selfish interest in contributing features or bugfixes), if you've written a CZ article, the chances are that once it's done you don't need to access it yourself because you already knew about the topic in the first place. But consider that for every article you write, there are tens or hundreds of articles written by other people. Isn't your completely unrestricted ability to use those other articles worth more than the possibility that someone else might make a (probably paltry) bit of money off the articles that you've written?
I think that if we want experts and all serious editors to contribute for free, then it is not so fair to release the content for money. Clearly, we do not that! This would directly push away potential contributors, would't it. We have a non-profit status. For-profit one would be demotivating, wouldn't it? So why we want to let others makes profits for free? What's the difference?
Certainly we want the content to be free at point of access, but that doesn't mean Citizendium has to abandon all commercial interests. There are more ways to make money than selling things.

As for motivation, it depends on what kind of commercial activities. If profits were being made and going in Larry's pockets (or the pockets of a select group of editors or constables) that would certainly be demotivating. On the other hand if Citizendium had commercial pursuits whose fruits were funnelled back into maintenance and expansion costs, I think most people would be all right with that as it takes off the pressure to always have donors.
As for third-party commercial interests, consider the Debian community as an example. It's officially a volunteer community, but quite a few Debian Developers (DD's) are encouraged by their employers to use paid office time to work on their Debian projects. In practice they are paid for working on Debian but it doesn't affect morale because Debian itself is treating all its members equally. Last year there
did arise motivational problems because it was perceived that Debian itself was soliciting payment for certain select members. In many ways it was for a sympathetic reason---the leadership wanted to ensure that the release managers would be working full-time to get the new version out before the end of the year---but many people felt aggrieved by it because for the first time Debian itself was making a financial distinction between contributors.
If we learn from that example we should see that it's all right to have third parties with commercial interests in Citizendium because their interests will lead them to help supply material. What we shouldn't do is
internally discriminate between our membership in terms of financial incentives.