Is net neutrality not important in a competitive market of internet providers? In my understanding, allowing ISP to throttle sites that use a lot of traffic is just price discrimination. The ISP will charge sites like Netflix, which will then pass the cost to Netflix consumers. So basically people who use a lot of data will get charged more--seems perfectly fine to me.

I understand the argument that in practice, the ISP won't build new infrastructure but simply put up roadblock to slow down the current speed. However, this seems like a problem only in the oligopolistic market of US internet providers. In a competitive market, putting up roadblock will cause an exodus to competitors.

So, am I correct in thinking that preserving Net Neutrality is not important in a competitive telecom market? Instead of fighting to preserve Net Neutrality, may be the correct fight is to encourage more ISP to enter the market.
Yes, if there were more competition then net neutrality would not be such a big issue. Any throttling would cause an ISP to lose customers to competitors.

Competition is a main assumption behind why markets work. However, in this case an ISP has market power which breaks the assumption. The market power allows them to easily put smaller ISPs out of business. 

Here is a link to a rather long article on how ISPs get this market power. Essentially, the reason is that starting an ISP is entering an economy of scale, which requires a large amount of capital to start: http://arstechnica.com/business/2014/04/one-big-reason-we-lack-internet-competition-starting-an-isp-is-really-hard/