I am fairly new to Bitcoin and Blockchain world, even though I keep reading forums here once in a while.

I want to understand few things w.r.t bitcoin code:

 1) Hoarding coins: How can hoarding excessive bitcoins be avoided? Lets say the total economy of BTC is 10 billion which converts to certain $ value at this moment. What if any govt or a conglomerate buys all of them or major share of coins, lets say 7 billion BTC. Won't they hijack the system? Won't they get powerful? Is it avoided in current system?
Also, is it possible to penalise hoarding in blockchain by code change?

2) Interest on lending coins: I see in this forum that people lend BTC for an interest with some collateral. Does that work purely on trust? Is there a legal angle to it?
And does the lender has ability to take collateral in case of non-payment?
    Is it possible by changes in code or otherwise to avoid people lending on interest? Like, 2 people can exchange BTC with or without interest. No body can stop that AFAIK. Is there a way to to convert interest lending into risk sharing model?