all of which require the second in command to speak up and perhaps even take action to prevent an acciden
All very vague in practice. Sure there are a few phrases the F/O can utilize and which may be published in company operations manuals. But "to take action to prevent an accident" is too generalised to be of any practical use. How exactly does the F/O take control of the aircraft if he thinks the captain is stuffing up? Most captains would use physical force against a copilot who said he was taking control of the aircraft. Very few manuals are specific on what measures a copilot should use to take control (and we are not talking about a captain incapacitation but a captain breaking safety rules and pressing on with a potentially dangerous landing).
The last thing that anyone wants is a fight in the cockpit between the two pilots over a perception the approach is dangerous. The F/O must be given concise advise on how to assume control. Words mean nothing to a reckless captain. Action must be taken to prevent a certain accident. Several operators advise the F/O to call a go-around and simultaneously raise the landing gear lever. No captain will then deliberately continue to try and land gear up. Of course there will be questions asked later but the main thing is the F/O has used his brains to force a go-around and thus save the aircraft from a probable accident. Of course there is a risk of a real gear up landing but providing the action is taken by the F/O to lift the gear well before the flare the risk is minimal and certainly safer than the alternative - a crash.