What have you to say against laughing? Cannot one be very serious even whilst laughing? Dear Major, laughter keeps us more rational than vexation.

[Was haben Sie denn gegen das Lachen? Kann man denn auch nicht lachend sehr ernsthast sein? Lieber Major, das Lachen erhält uns vernünftiger als der Verdruss.]

Gotthold Lessing (1729-1781) German playwright, philosopher, dramaturg, writer

Minna von Barnhelm, Act 4, sc. 6 [Minna] (1763) [tr. Holroyd/Bell (1888)]
    (Source)

(Source (German)). Alternate translation:

What have you to say against laughing? Can we not while laughing be very serious? Laughing keeps us more rational than sadness caused by vexation.
[Source (1884)]