At the time - we talking 2005-2008 - Crockford made a few net positive contributions to JavaScript and web:
1. He educated people about JavaScript the language and made it accessible to a large body of programmers as "a real language". Before him a lot of JS knowledge was obscure, and people were doing all JS programming by sharing random snippets here and there. Crockford showed how to build modular systems in JavaScript, how to avoid common pitfalls, how to reason about JS object model, DOM APIs and build larger systems.
John Resig was doing lord's work with jQuery, but his JavaScript book came out way too late to make a big difference. "Good Parts" on the other hand helped growing a whole generation of JS engineers. There were other books, too, that helped immensely, including John's book and especially Marijn Haverbeke's book, which eventually became a somewhat spiritual successor, and was "The Book" for JavaScript for about a decade.
2. He created the first linter for JavaScript and popularized the notion of using static analysis as part of JavaScript development process. For many years JSLint was the only game in town. And, on a larger level, JSLint introduced the whole notion of having a build / release process to JavaScript world. People joke about node_modules a lot, but before JSLint most teams simply FTP-ed sources to servers or were editing them live over SSH. Web programming was not a "real" programming, and Crockford helped change this perception.
3. Same goes to minification - he was the first one to talk about JavaScript execution as part of browser performance story, and created JSMin - the first minifier.
4. JSON format was largely responsible for ending XML dominance and let adopting new languages for server side development easier. I still remember times when I've been forced to only use Java because "the project required XML".
5. There's an argument that his "sticking to good parts" idea was harmful. He almost single-handedly killed ES4 proposal that would have add classes, modules, and other cool additions to JavaScript in around 2006-2009. But here's a thing: ES4 was a hot mess of seemingly unrelated proposals and features that played poorly together. Instead we spent extra years making the foundation of the language better, and then we still got all these and many other features through ES6 and further standards. Like many, I was pissed about ES4 at the time, but seeing where we are now with the language I believe he and Chris Wilson of IE did the right thing with "Harmony".
He was at the right place at the right time. Yahoo circa 2005-2010 did ground breaking job at making frontend development a separate proper discipline. They _invented_ the term "Frontend Development", they build tools for analyzing JS performance, they talked about coordinating work in larger teams and structuring large projects. Before them there were individual groups at a few large companies that were building large web applications (Gmail and Google Maps were the primary examples at the time), but the knowledge of how to do that remained hidden, tribal, and fragmented. YUI group aggregated it, published it and promoted it, making it available to a larger developer community.
They had a messy transition from YUI2 to 3 but the later was way ahead of its time. Crockford was not the primary author of the library, btw. The team was led by Eric Miraglia with significant contributions from Nate Koechley, Dad Glass, Ryan Grove, Nicholas C. Zakas etc. For many years it was one of the most popular libraries for building web applications in larger teams. It was eventually superseded by the arrival of frameworks like Backbone, Angular, React, etc. but for a period between 2006 and 2010 YUI along with Dojo were essentially acting as frameworks for us.
I agree, Crockford tends to sound like a naysayer, partially because his other ideas about compartmentalizing code, building more robust security into the language didn't pan out as he wanted, and things like Content Security Policy largely remain underutilized. But his work was important, his accomplishments are undeniable, his contributions were beneficial for JavaScript community at large.