Learn English – What do you call a person that criticizes your ignorance, but does nothing to help alleviate it

Suppose Alice and Bob are having a debate about umbrellas.

Alice does not like umbrellas for a few reasons.

Bob says

Of course you don't like umbrellas, you don't understand the real purpose of them.

Bob is pointing out that Alice has missed some fundamental concept. This not only tries to make Alice feel foolish, but now she is forced to play into Bob's hands by having to ask "Ok, so what is the real purpose of them?" Essentially conceding her ignorance.

Bob could have said

you don't understand the real purpose of them, which is to [ … ]

Is there a term to describe this style of debate, where someone is lead into conceding ignorance? (Of course, Bob's "opinion" might be wrong, and Alice may not be ignorant at all)

For example:

Bob, why do you use this style of [ ___ ] when debating? It doesn't help Alice out and only forces her to ask you a follow-up question, making it seem like she is appealing to you for help?

Is there a term to describe Bob (a noun)?

Bob is a [ ___ ]. It means he makes himself seem more knowledgeable and forces you to ask him a question, making it seem that he knows more than you do.

The only term I can think of is wise guy. This comes close. Is there something else?