I am not a lawyer and not trying to provide the following as legal advice, but here's something to think about. Ultimately, I don't think it's an issue that boils down to morals or ethnics, but rather simply legal. If you try to hide what you will be doing with user contributions, you are more likely to be viewed negatively in the eyes of the community, so I would suggest being more upfront with your plans rather than hiding them away in a legal document. I digress though.
Pretend I get level submissions from people and I use them in the game I release for sale. If this possibility is specified in the agreement for the beta (which I'd guess many people don't read), is it in any way wrong?
You should also need specific terms that apply to the process of "content submission" in addition to the normal terms applied to the game/tools themselves.
In regards to the latter, your terms should say what people can or can't do with the content they create with your tools. E.g., if you provide people with a level editor, clearly specify if they can only use it for non-commercial purposes, if they are allowed to re-distribute the content, and so on. There's a lot to consider there and it's handled a number of different ways in different scenarios.
In regards to the former, you open up another can of worms when it comes to accepting user content, especially if you plan on publishing it or redistributing it in any form. For example, and I'll use an excerpt from the GameDev.net Terms of Service
c) Customer warrants to Provider that Customer has all necessary rights to store, reproduce, license access to, and otherwise use the data contained in each of the Customer posted content for which Customer utilizes Provider's Software and Services.
d) Customer acknowledges that Provider's software stores customer data, personalization settings, and other Customer posted content. Customer hereby grants to Provider a fully paid up, non-exclusive license to store and maintain such data for the limited purpose of providing a public forum.
'c' is vital in terms of ensuring users have the necessary rights to provide the material and 'd' is vital in establishing what that material can be used for once GameDev.net has it. If you look up the ToS for any game publishing platforms or application stores, you will see similar. Some sites reserve the right to feature or use your stuff for purposes of promoting their site and so on. It should be noted though, you are still ultimately responsible for the content, even if someone breaks your ToS to provide you with it.
In other words, since you are accepting user created content, even though it is done with your tools, there are still "rights" issues that have to be considered. If your levels allow people to supply their own textures or models, then you would need to ensure those textures and models are not being used from a rights violations. Perhaps specific level designs are made that would infringe on trademarks or one thing or another. There's a lot of considerations.
In either case, you are setting yourself up for a lot of potential legal problems if you simply use user contributed content directly in your game. You would have to verify and ensure you have all the necessary rights to use the content first, which in itself, might be too much work to be worth it, to avoid issues down the line when someone sees their stuff in your game. People obtaining and using content that contains rights violations is a totally different issue, out of your control (from a non-technical standpoint, e.g., not having DRM mechanics built in).
If I were you, and you were worried about these things, you simply don't bundle any user contributed content with your game. You create a website that allows for people to share and download maps, taking into consideration DMCA provisions and the steps necessary for addressing copyright complaints so you are fulfilling your legal obligations. Here is one such page (random, no affiliations) that will give you an idea about that: Reducing Company Website Liability - Steps to Verify DMCA Safe Harbor Compliance
That way, if anyone has any copyright claims, they need to follow the process and give you the appropriate time to respond vs. just sending out a C&D or filing a lawsuit for the violations. Here is another page (random, no affiliations) that cover this as well: How to send Cease & Desist and DMCA Takedown letters to sites infringing your copyright
Of course, a lot of these things depend on how your actual level editing pipeline works. If you are talking about a 2D game with a fixed number of sprites to use, and it's a matter of a map format that uses only numbers to represent the tiles and users cannot add any custom images or sounds, then you won't have to worry about hardly any of these things. In that case, it's simply a matter of establishing the terms of what you can do with the content once a user submits it to you.
On a side note, and I'm sure you are familiar with the game, StarCraft 2 took quite an interesting path when it comes to content creation by keeping everything server sided. Even with that model though, they still have to maintain a clear copyright infringement policy
consistent with what was previously mentioned.
And as always, you should consult a lawyer!