Some say that this is an additional rule, because with any rabbinic doubt, if you want to be stringent, fine; whereas with the rule of being lenient regarding doubtful blessings, you cannot be stringent because of the prohibition of “Do not take [God’s name in vain].”
What does the Rabbi think of this answer?

If so, then this discussion has no importance at all.
After all, everyone agrees that this is part of the general rule of rabbinic doubt (since in the case of Grace after Meals we do not apply it). And everyone agrees that one may not be stringent because of “Do not take [God’s name in vain].” So what practical difference is there whether it is a separate rule or not?

Right, there’s no practical difference, but they stated this as a separate rule so as not to confuse people, so that people would say to themselves, “Wait, here this is a separate rule, there’s something special here—don’t forget that you’re not allowed to be stringent”…
Haha, that does seem too weak—you’re right.

I didn’t mean only to say that it’s too weak (though it really is weak. They should have formulated it: in a case of doubtful blessings, be stringent—not to recite the blessing). Even if it could be true, what is the point of dealing with it? What do you learn from the conclusion that this is a new rule?

Sorry, I didn’t understand. If it is true that they stated this rule so that people would pay attention that they should not be stringent and recite a blessing here, then fine—I, as a Torah scholar who learns all day and knows that one should not recite a blessing when there is doubt because of “Do not take [God’s name in vain],” don’t learn anything new from there being an additional rule, but still there is an additional rule for the reason above, so that people will pay attention? In short, I didn’t understand the second part of your last reply.

I’ll say it again. I said two things:
1. It does not make sense, because if that is the explanation, then the formulation of the rule is not good.
2. Even if this explanation is correct, and indeed the Sages formulated a separate rule for that reason, why is this discussion important for us? It has no importance whatsoever. Here I was not challenging the explanation, but rather the importance of the discussion you are conducting about it.