No, the Maryland law is not contrary to federal law on this. The reason is that you misstated the issue. Federal law does NOT say you are allowed to make recordings as long as one party consents. What the law says is that it violates federal law to make a recording of a private conversation unless at least party to the conversation consents. In other words, federal law is not conferring on you a right to make recordings so long as you have consent of one of the participants. It is simply saying the federal government will prosecute you if you make a recording in which you do not have the consent of at least one party to the conservation. Because the federal government has not given you a right to make any recordings, the states are free to impose more significant restrictions on recordings if they choose. Maryland and a number of other states have chosen to require the consent of ALL parties to the recording. That does not violate the Constitution or federal law in anyway. If you record a conversation in Maryland with the consent of just one party, the feds won't prosecute you because you have not violated federal law, but Maryland may prosecute you because you have violated Maryland state law.
There doesn't have to be an injury to anyone. If you commit an act that violates a criminal statute, you may be prosecuted and punished for that act even though no one was harmed by what you did.
Then I guess it's a good thing you are not a lawyer.If you were a lawyer advising your clients with the position you gave above you would put your clients at risk and perhaps get you dinged for malpractice. If a statute says it is illegal to make the recording itself, then simply making the recording violates the law regardless of what use you make of the recording. If it was the use that mattered, the statute would say so; Congress and state legislatures know how to write such statutes after all. It's like a law that prohibits running a red light. I have seen people argue that it is not illegal to run a red light if there is no one else around because then there is no risk of an accident and no one is harmed. But that is clearly not what the law says. The law says it is illegal to run a red light. Period. If you run a red light you may be prosecuted and fined/jailed even if there was no other car around in a 100 mile radius. It is the same thing with these evesdropping laws: most of them make the act of recording it a crime in itself, and thus under those statutes it is irrelevant what use you made of the recording.

If you were a lawyer advising your clients with the position you gave above you would put your clients at risk and perhaps get you dinged for malpractice. If a statute says it is illegal to make the recording itself, then simply making the recording violates the law regardless of what use you make of the recording. If it was the use that mattered, the statute would say so; Congress and state legislatures know how to write such statutes after all. It's like a law that prohibits running a red light. I have seen people argue that it is not illegal to run a red light if there is no one else around because then there is no risk of an accident and no one is harmed. But that is clearly not what the law says. The law says it is illegal to run a red light. Period. If you run a red light you may be prosecuted and fined/jailed even if there was no other car around in a 100 mile radius. It is the same thing with these evesdropping laws: most of them make the act of recording it a crime in itself, and thus under those statutes it is irrelevant what use you made of the recording. 