Bip300 adds an opcode that allows a sidechain to store bitcoin as a security for a project. The project could be fo something like an Etherium clone, or a better version of lightning network. You have to choose to buy in , it does not interfere with bitcoin. It does not change anything else about the way bitcoin works.

It prevents a rugpull because to withdraw funds from the pegged bitcoin takes several months and is visible to everyone.

There are many benefits. Future changes to bitcoin can take place on L2 instead of L1. Users get to choose what they want instead of a few devs.

If you don't want it, it doesn't affect you

I have yet to see a good against argument that is not just a preference for not putting ones own money in a side chain.