Ask HN: Why am I not permitted to crawl HN?

I was trying to crawling all articles on HN to do some data analysis stuff just for fun. But it seems like my IP is banned after I've crawled a few hundreds pages(at a very low rate of a few seconds per page).

I believe it would be a good thing if HN allow people to get its data just for some fun side-projects, or even better make it publicly available. It would encourage the hacker culture to just do some fun and innovative things.

What do you guys think?