I would always encourage using a library over not using one - if you're not using a library you're just going to end up making your own anyway to "save time" - might as well start with something everyone already knows. If your project is also going to be something that a lot of people touch, you don't want to be using your own solution or a lesser known solution just because it's neater - that would be a waste of time.

So yeah, in my opinion if you opt to use your own solution or a lesser known one, I'd say you're at least a bit of an asshole because 1.) you're assuming you know better than the majority of people (who don't have a problem with using jQuery) or 2.) you're wasting everyone's time by forcing them to learn something new when there's a perfectly fine solution already available.