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.