If a union isn't needed form one anyway, now you only have to do the contract negotiations once instead of doing the same shtick of "This is the payraise I can offer you, please sign if you are fine with that". There is literally no downside to having a union anyway if you are of the opinion your employees don't need one.

Now if you actually think a union would harm you as a business owner that equation changes and you have every incentive to invent reasons why a union is unnecessary anyway and how unions only exist in companies with crap working conditions. (Cannot speak for the US but at least here some of the best companies are well regarded by employees because of the union, not despite of it.)