The BTC crowds does not like SPV security and I think the BCH and BSV communities tend to not fully understand the argument. Let me present it here for you:



SPV security cannot detect certain changes in consensus rules. For example, a miner can create money for himself, he can increase the block size and he can even fill the block with random garbage bytes plus some transaction data.



That's because the SPV node is presented a proof of a) the POW and b) the existence of his transaction in a block. But whatever else is going on in that block, or in the past, is undetectable.



So if 90% of the network run SPV and the miners change the rules (e.g. blocksize increase) those nodes will simply follow those new rules without consenting.



Those 90% form the economic majority. This forces the remaining 10% to also accept the new rules because the old chain is worthless.



For that reason, it is thought that at least 80% of the network should run full nodes. Requiring a small blocksize is just a consequence of this.



My take: There is no realistic case where this is a problem. It's fighting windmills.