What does the author imply by using the phrase “open to attack” for the element of worship in patriotism?

Question

Source: https://csatprep.files.wordpress.com/2015/01/rc-exercise-1.pdf

Patriotism is a very complex feeling, built up out of primitive instincts and highly intellectual convictions. There is love of home and family and friends, making us peculiarly anxious to preserve our own country from invasion. There is the mild instinctive liking for compatriots against foreigners. There is pride, which is bound up with the success of the community to which we feel that we belong. There is a belief, suggested by pride, but reinforced by history, that one’s own nation represents a great tradition and stands for ideals that are important to the human race. But besides all these, there is another element, at once nobler and more open to attack, an element of worship, of willing sacrifice, of joyful merging of the individual life in the life of the nation. This religious element in patriotism is essential to the strength of the State, since it enlists the best that is in most men on the side of national sacrifice.

(Note: This passage appears in Bertrand Russell's Why Men Fight; however, this should not be necessary to understand the passage, which was quoted by itself in the example question linked above.)

The example question asks

What does the author imply by using the phrase “open to attack” for the element of worship in patriotism?

Options are:

• This element is unnecessary in some instances of patriotic behaviour
• This element will call for various acts of national sacrifice
• This element has no historical basis yet it is important
• This element can cannot (sic) be justified on rational grounds

The answer key indicates that the last option (the element cannot be justified on rational grounds) is correct.

The analysis is not quite clear to me. I want to know what this sentence actually implies:

here is another element, at once nobler and more open to attack, an element of worship,

Answer 1

"Open to attack," in this context, means that this particular piece of the feeling of patriotism is vulnerable or defenseless to questions asked about it. (I couldn't easily find a dictionary that defined "open to attack," but thesaurus.com links it to defenseless and vulnerable, among other, similar words).

The worship-like element of patriotism, then, must vulnerable to something according to the view portrayed in the quoted passage. Since this is a standardized test with only four possible answers, we can consider each of them to decide whether they fit.

1. "unnecessary in some instances of patriotic behaviour" does not mean that this element is vulnerable to an attack; it means that it is not always needed. Next!
2. "will call for various acts of national sacrifice." This option can be a little confusing, because it might mean that it leaves patriots vulnerable to put themselves in danger, to sacrifice themselves for a national benefit. However, on further thought, this describes a vulnerability in the patriot, and not in the belief of patriotism.
3. "has no historical basis yet it is important" does not (only) describe a way that this part of the belief is vulnerable. This statement made me think a bit, because it does kind of present a vulnerability -- that there is no historical basis for this element of patriotism. However, the second part of this statement, "yet it is important," is not something that is part of the definition of "open to attack."
4. "cannot* be justified on rational grounds" is a major vulnerability in patriotism. If it cannot rationally answer questions about it, then it can be described as "open to attack" from those rational questions.

By process of elimination, then, the answer must be number four.

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*I was going to correct a typo in your question, but then found that the typo was also present in the original -- the question actually does state that "This element can cannot be justified on rational grounds." You may be better served using other study material. I haven't really thought about your other question much, but many of the commenters there posit that all the choices for some of those questions are wrong. Good luck.