I try to give you my opinion on each paragraph.

1. I don't understand/see how inscriptions could be used as backdoor to attack bitcoin. Tell me more.

2. There is no junk in the blockchain. If someone pays the fee it's not junk. It might be junk for you but not for the one who pays the fee. If the amount of "junk" increases, the fees getting higher but this is OK because this is called free market. Bitcoin will survive and if not, Bitcoin was not worth to survive.

3. Yes, Bitcoin transactions will be extremely expensive in the future. We will not be able to make onchain transactions. That's why we will use second layer solutions like lightning. And to go back to onchain, we will bundle hundreds or thousands of transactions to split the costs. Or we will find other solutions. And if not, Bitcoin was not worth to survive.

4. I don't think so because of point 2 and 3.

Taproot is useful for many things and increases privacy for on-chain transactions. These same primitives that power inscriptions are also used for Taro, which enables stable coins on Lightning Network.

Also, Bitcoin is a permission-less network. So you may think these transactions are worthless, but to someone else, they are clearly not.

If Bitcoin dies because of JPEGS, it was never going to win. Also inscriptions may provide a price floor for transactions, but they will not compete seriously with movement of money in terms of sats/vbyte.

Also, fee rate pressure may push more into Lightning Network and encourage further expansion of this tech, which will be necessary if we hope to scale Bitcoin globally. Blockspace is insufficient for most people to use Bitcoin on-chain in a hyperbitcoinized world. This was already true before taproot and inscriptions.