It’s a good contender, but the lamppost has also been in use in service of political ideology more recently than the guillotine has (see Nazi summary “justice” at the end of WWII) and isn’t designed for a single violent purpose. Due to the first aspect, I don’t think it would satisfy the criteria of the pearl-clutchers here.
On the other hand, as others have pointed out, it has Edith Piaf going for it.
