Houses were build on land that belonged to some one else and now they are getting knocked down.

Yes, this is essentially it. It's not that (for the most part) the land is owned by someone else, It's that It's occupied territory. It's a good thing because these settlments are illegal not only internationally, but also according to Israeli law. They don't benefit Israel (or the Palestinians) in anyway, and the main reason they're allowed in the first place is thanks to Israeli far-right and religous parties in the Knesset.

They're dangerous to build and protect, wasting the IDF's time and resources and putting guards at risk. Most normal people won't live in them anyway, only religous fanatics or poor people who don't mind the danger. They cause allot of unnecessary international and local problems, aswell as being a sticking-point for many would-be supporters (whether individuals or countries), and overall a legal and PR nightmare.