3) The network can be spammed with large blocks. But what is an effect of that spam, how dangerous is that spam for Bitcoin blockchain? .
3. Blockchain size growing quickly, more resources required to verify blocks/transaction, etc.
Also the network being easily spammed means that there's little to be gained from an increased blocksize.
A 1MB block with zero spam is just as effective as an 8MB block with 7MB spam, but way less efficient. (the numbers being just an example; as mentioned by ETFbitcoin the blocksize limit is now measured in weight units leading to an effective blocksize of ~1-2MB)