When Steam first came out, people didn't just hate the idea of Steam constricting their games, they hated the actual implementation of the client. The client was bloated and unstable, and the Counter-Strike community in particular was upset by the fact that Steam was being forced on them even though it didn't confer any significant advantages over WON. During the first week, people had authentication issues with the client not allowing them to play games that had previously worked fine. At one point, someone cracked the exe to not use Steam and the result was better game performance, which was further evidence of how poorly the client was implemented.

The main thing that people like about the Steam client now, as you mentioned, are the client's community support features. People also like the Steam store's frequent discounts. Steam community integration didn't exist until late 2007, and 2007 was also the first year that they did a major holiday sale. Before that point, most people were either neutral on the system, or disliked it because the client was a waste of resources. Its memory footprint was big enough to make a significant performance impact on older machines, which is significant when you consider that Counter-Strike, the most popular game on Steam at that point, was a game from 1999.

People eventually came to like Steam, but that wasn't until Steam began functioning as a service that added value to a product, rather than an impediment that devalued a product. The Battle.net 2.0 is plagued with many of the problems of the original Steam client, and it confers very few of the benefits that the present-day Steam does. People don't just hate the idea of it, they hate the very client itself and will continue hating it until Blizzard does something to fix it. Forcing it on the playerbase when it is still in its current unpolished state is making a lot of people very upset, and reasonably so.