No, you're right, though it is not the end of the plant it can suck all the energy out of the crown and then the crown never recovers. Take off this flower stalk, the best way to propagate from a crown is to split it or take off one of the rhubarb stalk 'nodules' when they first start to bud - you can cut this off with a sharp knife taking some of the crown and get a new crown this way. If you let it flower, it will just be wasted - and sap the crown of energy. I was always told to take them off.

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Best wishes
Andrewo
Harbinger of Rhubarb tales