There are two schools of thought when it comes to what is often known as "fake Lego".

There are the products like these, where the same style of brick is used, but the company produces and releases their own unique designs, and in some cases, like Mega Bloks, they even get their own licenced products such as Halo. I think there is room in the marketplace for things like that.

Then there are the other side of the industry there are companies such as Lepin who blatantly steal other people's intellectual property and release it themselves. Those types are actually detrimental because they drive prices of genuine licenced products up (companies like Disney, Marvel, DC etc charge more for the licensing fees to cover the loss of royalties to the counterfeit products)