Knots people don't want to relay transactions they consider spam from their nodes. However having filters on their personal nodes can't actually stop it so it's mostly symbolic (they might disagree with this).

Core is removing the filters because it creates friction in the network. It gives large miners an advantage as they have the resources to build systems that accept spam transactions directly for higher fees, reducing the competitiveness of smaller miners and contributing to mining centralization. Also people that run filters will be at a disadvantage when calculating fees from their own mempools because they won't know about the spam transactions. Additionally removing filters disincentivizes other novel and potentially harmful ways of embedding data like custom addresses that contain the data in the address string.

People feel they are being forced into this change by core and don't want to give up the option to set local mempool policy on their nodes. Core is by far the most dominant implementation and having a small group of devs making these decisions is concerning. Questions have arisen about conflicts of interest that are totally valid, and resulted in bans on the GitHub discussion of those expressing those concerns. Censoring opposition is not a good look and turned many people against the core devs, and also caused the conflict to spill out across other social media.

That's about the gist of it. I've been following this as closely as a pleb like me can. I was against core at first, but I've come around to their arguments and think the stability and smooth functioning of the network is more important. Filtering spam at the node level is ineffective and creates unintended consequence that are harmful to the network. Also even though I call it spam, there is potential for useful L2 stuff to be created that furthers bitcoins mission as well.