Do you need to "drink the kool-aid" to be successful?

I've had this conversation with a few people I know in sales and I think it's an interesting question. Do you think that in order to be successful in sales, you need to "drink the kool-aid"?

Sure, all of us are in sales because we have solid negotiation and persuasive skills, but to be truly successful at any company, do you need to be bought in to the product/offering? I believe that the most successful reps at any company are the ones that believe in the product wholeheartedly and that is why they are able to make convincing arguments as to why someone else should buy.

Follow up question here if you disagree, do you think it's a bad idea for sales people to be that invested? Why?