Can I go off on a stranger and tell them we don't need any input for my wedding?
Was the stranger giving good advice about your wedding?
Yes, but I don't need to hear someone ramble on showing how smart they about weddings.
If the stranger was just trying to help with advice on your wedding, you are being inconsiderate by telling them off. You don't have to take their advice, but be civil in your discourse with them.
Freedom of speech.
Yes you have the right to tell someone to not give you advice but if they're trying to help then try being kind in the way you ask them to stop. Maybe you don't want to hear what they have to say now but you shouldn't burn a bridge if they're knowledgeable about a subject you want to learn more about.