With PoS, the more coins you hold, the more power you have over the network. Now think of the huge exchanges such as Coinbase and Binance — think about how much power they'd have. Bitcoin with PoS is simply a disaster.
Exactly. However, it is important to note that monopoly will exist in most systems, if it is fundamentally based on the virtue of whoever having more resources being in an advantage.
The problem with PoS mainly lies with how it doesn't require consumption of resources during the mining process. If the process doesn't cost the miners any resources, then there is lesser incentives for a miner to be honest. PoW functions with the fact that there is so much resources being consumed during the process and it would undoubtedly cost the miners a lot if they were to try to attack Bitcoin. The resource consumption is what keeps Bitcoin secure, if you can't come to terms with it, you should probably criticize the financial systems around the world for their electrical consumption as well.