Living in Scotland, I guess room temp is probably okay to leave butter out (usually have the thermostat set to 18C)
I wouldn't do it, though, because you can't cut soft butter, only spread it.
My preference is to have good salted butter nice and cold in the fridge. When making toast, I usually hold the knife over the toaster to heat it up then cut off slices of butter maybe just under 1mm thick and place them on the toast immediately it comes out of the toaster. The butter then melts straight into the toast with no spreading required.

Of course, you need to get a good quality, salted butter because otherwise it tastes terrible.

Edit - of course, Scotland is famed for the high proportion of heart attacks in the population. Hey ho!