I believe you already got several sensible and polite answers for your question. However, I figured I could give some extra commentary on your point of view. This will be a very "I"-based answer and risks being ruled out as an opinion (it is), but I hope it brings some value.
I am not a fan of formality for the sake of it, as I feel it just adds complexity and arbitrary rules for a non-existent problem. In particular, I feel awkward when it comes to last names or titles. Whenever someone starts a conversation with me and addresses me by my last name, my smile automatically vanishes (already as a reflex) and I ready myself for a stressful conversation where my manners will matter more than my thoughts.
The message conveyed is clear: "we are not equal and I expect you to treat me with deference on the basis of some arbitrary achievement". Sometimes, this "achievement" is being born as part of a family (that's what a last name represents, and in some cultures, like mine, it carries more weight than it makes sense): "oh, so you are related with...". Sometimes, the achievement is somewhat more relevant, as a degree (Ms C, PhD...) or a certification (oh, how popular they are in my field of work).
My problem with that is that it brings a lot of weight on the basis of something that is not particularly relevant to determine the quality (I don't like the word, but it is what the titles aim to reflect) of a person, or even its academic worth. I have (as you, in the academic field, probably have) met more than one or two Ph D graduates that fail in life as human beings (in terms of common decency, respect or even skill on their field), whereas some diploma-less people have been nicer and more knowledgeable (and more willing to share their knowledge!) in more than one occasion.
First names, on the other hand, are a sign of empathy. They can break invisible barriers, make people closer and reinforce their role as individuals (as opposed to "member of a family", "owner of a certificate") and, altogether, feel less forced.
I do not mean to deny the fact that in some cultures and contexts it might be more appropriate to use last names. However, I want to highlight that your assumption that it is a sign of respect might be misleading and not always hold. And in particular, as some other answers mentioned, keep in mind that the stiffness of such rules keeps relaxing over time. Choose the way of addressing that leads to a more comfortable conversation environment (for both of the speakers!) and mind less about arbitrary preferences!