Go to basic principles and analogies
Ask the person who questions why someone would 'Google' anything if they have ever gone to a library to obtain some knowledge that they did not possess before. If so, ask them if they think internet services like Google Books have improved access to books and information. If they say 'yes' then you can say that digitization of such books has afforded people the luxury of not having to take a prolonged trip to the library in order to access the same books (however, see real-life caveats below). This could be A) cost saving if fuel would need to be consumed to get to the library, and B) time saving, since it is also faster than physically going to a library. If they concede that then they have conceded the value of the internet and digital resources being searchable online.
How much and what kind of knowledge are you really obtaining?
However, there is the flip side question of the quality of the resources you are accessing and also whether 'quick lookups' do anyone any good in terms of how much knowledge you are obtaining. This goes as much for physical resources as digital resources.
As for amount of knowledge and the time expended obtaining it, consider the following scenario. If you did not study for an upcoming history exam and went to a brick & mortar library and cracked a book on the subject that you are to be tested on for only 10-15 minutes would you expect to understand the material comprehensively? Would you even hope to understand it accurately, if you were reading summaries rather than specific and detailed facts? I would expect not. Yet some will spend only that amount of time or less when reading internet resources.
Then there is the quality of knowledge element. For example, There is a significant difference between accessing a common public encyclopedia open to being edited by anyone, such as Wikipedia, and accessing online journal repositories like JSTOR geared towards academic research. I too would provide critique of anyone who thinks they can simply peruse Wikipedia on a non-trivial subject and then claim they've adequately got a handle on a subject, especially a subject of academic investigation and research. One anecdote could be that Ph.D. Dissertations are not based off of citations of Wikipedia but more often peer reviewed literature which is not always free or readily accessible.
Free or pay-for knowledge?
On the topic of "free" knowledge (both in terms of access and price) this brings up another point. As wonderful as the internet is it is a complete myth that for any subject of relevance there is an educational resource completely available on the internet for it. Only a small fraction of the world's books have been digitized, stored, and made accessible (although Google Books and HathiTrust have done wonders in that department). Being someone who researches rather niche academic subjects myself, I find myself spending several hundred dollars a year purchasing books which have knowledge which is not yet freely accessible on the internet. Also, even with the availability of pirated books (legal issues aside), if all college text books (say) were available online for free then few would pay for expensive hard copy books, and the college book industry would collapse (not to mention all book sellers as well: Amazon, Barnes & Noble, Books-A-Million, etc.).
That is all to say, much knowledge is still locked away in physical copy books and other materials which cannot be found on the internet, whether or not they are free to access (at your local library) or are "behind a paywall" (books you must purchase to obtain access to). Therefore, anyone who thinks that they have access to the entire sum of human knowledge just by having access to the internet has not been paying attention and in fact has been infected by a bit of hubris no doubt, falling victim to misinformation and naiveté.
Oh, but how I wish it weren't so, for then I wouldn't have to break the bank to purchase academic books which have specialized knowledge locked away in them.
Just another tool
So, with all this under consideration I would summarize by saying that internet is simply a tool for what humans have always been doing: obtaining knowledge. As such is neither more nor less respectable than ways of doing so that do not involve modern digital technology.
In the end, think interpersonally and contextually
If running to grab an actual book to gather information in the middle of a discussion might, in fact, be disruptive then there is a chance that even the far quicker access of digital data might do the same. That being the case, that may be why some people get annoyed and wonder if people can't "think for themselves" and have to (as they perceive it) always run to an external source.
However, if the discussion is not regarding a matter of purely abstract reasoning based on prior knowledge and is in fact dealing with empirical facts then you can try to justify the access of potential sources of facts on the internet that are relevant to the topic at hand. So, in the end, there is no blanket endorsement or prohibition that should be given for using such tools in a discussion and it will vary based on each circumstance and also depending on how socially agreeable or polite you wish to be.