I'd say disagree more than look down upon. Obviously, it depends on the person, but I definitely know some non-halachic converts who are super duper awesome and extremely knowledgeable about Judaism. It's simply that, by my standards, they've never undergone a valid conversion.
Orthodoxy does not see the other groups as correct. Officially, Conservative and Reform are more pluralistic, but in reality, things often don't play out that way. My grandma's Conservative rabbi routinely says very anti-Orthodox things, and my Reform ex-boss did not accommodate Orthodox employees taking time off for holidays even to the extent required by American law. On the other hand, the Reconstructionist rabbis I know tend to be supportive in a "whatever makes you feel fulfilled" sort of way. Mostly, there's not really terribly much interaction between movements. I grew up in a combination of Conservative and Reconstructionist communities, and rarely did anything with the Reform community. This probably varies with the size of the community, but mine is large enough that there's less need to get together for things. Mind, there are some organizations that unite all of the Jews in my city, but they're usually charities. And there's plenty of people involved in multiple Jewish groups.
As someone who became Orthodox as an adult, I have a lot of interaction with non-Orthodox Jews, because my family is mostly Conservative, Reform, or not Jewish. But if I did not have non-Orthodox family, I probably would have much less contact with non-Orthodox Jews. Not out of dislike, but simply because it's much harder to keep up a friendship if one person keeps kosher and the other does not (I'll note that some Conservative Jews do keep kosher, but none of the ones in my family do. My in laws do, which makes visits much easier).