With 2x, the worst case size is ~8 MB. We don't know how such large blocks will effect the network. It could increase orphan rates, it could cause many nodes to drop off of the network because they can't handle the additional load. We don't know if the network can handle such larger blocks. Just because your internet connection can and your machine can handle the load does not mean that everyone around the world who is running the node can. They may be restricted by things like the Great Firewall of China which may find larger blocks easier to spot and thus make Bitcoin easier for them to block entirely.

Furthermore larger blocks can lead to miner behavior that is detrimental to the network. If the mempool is constantly cleared by a new block, then miners may be more incentivized to perform fee sniping instead of moving the blockchain forward. That is not good for the network.

Why does the "base block size" need to be bigger to stop spammers? You don't think they aren't going to also use segwit? Spammers can use segwit and pay less in fees than they would with a non-segwit transactions, and make more spam that fits in a block. If you double the maximum block weight, you depress fees even more and let spammers pay even less to spam transactions.

Having more transactions on chain does not necessarily correspond to having more transaction fees in a block. If the general idea is that larger blocks will decrease fees, then that means that more transactions need to be made at a lower fee rate in order for total transaction fees to match the fees for when blocks were smaller. Currently transaction fees are pretty low anyways except the times when people are spamming transactions (and it is very noticeable when that happens because the number of transactions in the mempool at a certain fee rate inorganically shoots up).