No, it's a fact. The West is not going to risk the Apocalypse for Ukraine. Unless Russia directly attacks a NATO country, there is practically nothing they can do to trigger a war between NATO and Russia.
Why irresponsible? My take on it was that message was aimed at Ukrainians living in the UK who wanted to go and fight. Your average Brit isn't even going to humour that idea.
If Putin is launching nukes, it has nothing to do with Ukraine anymore. The choices are “do we let a madman play with nukes or not?" I think the answer is pretty obvious.