Merely listing prices (without an associated automated payment form which could imply a contract was en force upon successful payment) doesn't actually force you to do business with anyone. It would however 1) deter requests for unpaid work by giving them an idea of what it would cost to get what they're looking for and 2) give you an idea of the demand for said services and could give you a warm lead which you can then choose to pursue formally by getting the necessary business structure, legal/business advice, etc.
In some cases it could. If you want to say "we categorically don't do X for ethical reasons", that can sometimes be more easily defensible in a way that "we have a standard price for doing this, but we don't want to do it for you in particular" may be harder to defend. (Even though I think both should always be possible.)