If the Protestant is honest, he will agree that the sacraments matter. Well - even if he doesn't functionally think very highly of the Eucharist, a high opinion of the value of Baptism is pretty-near universal among them (and this is a good thing).
However, if the Protestant is honest, he will also have to agree that he and his fellow Protestants have radical disagreements about the sacraments. We need not rehearse these disagreements here, having done so in other posts; besides, these are fairly well known.
A question arises on account of these disagreements among Protestants over things that (as they agree) matter: how reliable is their method for arriving at certainty about what God has revealed, if it does not result in agreement among them about things that (as they agree) definitely are matters of importance? It's one thing if there is disagreement about food and drink, as may be argued from Romans 14. It's quite another when there is disagreement (as there certainly is) about things that certainly do matter, like the sacraments (for example).
The first observation that I'd like to make here is that if their method for extracting truth from the Bible fails so badly that they do not and cannot agree about important things like the sacraments, then it is an inherently unsafe method. We need to know beyond question what it is that God would have us believe and do when it comes to matters of importance like the sacraments. Because the Protestant method does not deliver this certainty to us, it cannot be correct. It is a false method.
The second observation I'd like to make is that if their method demonstrably fails in these areas where their disagreements are embarrassingly obvious, there is absolutely no reason whatsoever to believe that the same method has been successful in those areas where they happen to agree. After all, if it fails to provide certainty in the one case, and the same method is used in the other, we have to concede - unless the truth is a matter of majority vote! - that it cannot provide certainty in any case. At any rate, on their own terms they have no basis for knowing whether it has successfully delivered the actual truth (unless the truth is a matter of majority vote!).
Actually, if the Protestant could demonstrate (using this same method) that the two cases actually are different in some significant way, then he could perhaps save the case where they all agree. But I see no way that this could actually be possible: there will be no way for them to demonstrate, without question-begging, that the case where they all agree is actually different from the case where they disagree.
For these reasons it is an incoherent (and therefore invalid and false) method, which does not and cannot deliver certainty.