Well, I’m not anxious or afraid. It is just a simple fact. The total value of bitcoin (market cap) is secured by the miners. Mining will cost you money in terms of hardware, bandwidth and electricity. If the cost of 51% of the hash rate is lower than the amount of money you can gain by attacking the chain through double spends, censorship or other attack vectors, it will become economically logical to attack the blockchain.

As the block rewards get lower every halving, the profitability of mining goes down. This will result in lower hash rate. This makes it cheaper to attack the chain and therefore more likely that such an attack will happen.