The thing you have to understand about the ardent small-blockers is that they really genuinely believe they are protecting Bitcoin from a very real existential threat. If Bitcoin's security properties get diminished, there's no going back, no undoes or fixing the problem. It is a permanent change that irreparably weakens Bitcoin. What you view as overly zealous conservatism they view as appropriate caution given the risks involved. Now, I happen to think even given the risks that they are overly conservative, and I support a hard fork blocksize increase... but I don't begrudge them for sticking to their guns when from their point of view, they are defending Bitcoin's very existence from what they perceive as a very real threat that might destroy Bitcoin.
Irrational fear. They just want the fees to go up and drive users off-chain onto LN controlled by outside centralised entities.
IMO the current bitcoin mining operation is centralized by the likes of Bitmain and some mining pools. As far as I have read, LN would lower the fee a lot, off-chain transactions would lead to more user privacy, and exchanges would not be prone to hackers. Payment channels/hubs getting centralized is a possibility, you would need a lot of revenue backup to operate hubs and some big players like Coinbase would dominate, but the same thing is happening now. Hard fork is not backwards compatible, and with the rate bitcoin is getting adopted increasing blocksize would be a temporary solution, what happens when limit is reached, another hard fork? Segwit alone is not a scaling solution, LN is. If it could be said that LN would lead to centralization then it is not wrong to say that bigger blocks would lead to centralization simply because only a few miners would be able to afford to run full nodes, centralized entities.
As a user, I do not see why not LN. I am not against bigger blocks, but LN could be the permanent scaling solution. Using temporary solutions and letting bitcoin users go through periods of uncertainty would be bad to the community as a whole. The prolonged scaling debate and increased fee has already affected bitcoin, alts have increased in value during this time, continuing this would be illogical.