Credit card companies literally pay me to use credit cards. It costs me nothing, and the lack of instant settlement only protects me as a consumer. Why would I prefer to use BTC if it means paying fees, waiting for settlement, and having no consumer protections? Because it's better for merchants?
All fair points, but it goes both ways. Sites like Bitrefill pay me to use bitcoin. I can get cashback (or satsback, if you will) of up to 6%, which is far more than I can get from a credit card, not to mention that often I can buy cards for a percent or two cheaper than their fiat value. That more than offsets 5 cents in a transaction fee.
If merchants can save so much by avoiding credit cards, they ought to be giving sizeable discounts for BTC payments. I don't see why consumers would be interested otherwise
A number of local places I regularly spend bitcoin offer between 5 and 10% discount on their listed prices for paying in bitcoin, exactly because they don't get hit with outrageous fees from credit card providers and banks. And even if they didn't, I would still continue to spend bitcoin with them for the primary reason I got in to bitcoin in the first place - I don't want a third party credit card company or bank monitoring all my transactions and deciding whether or not they are acceptable. It's my money, and I'll spend it how and where I like.
What other options are there that are widely considered safe and adequately tested? Why would this be limited to the opening and closing of Lightning channels?
I don't think we could call Lamport signatures safe and adequately tested at the moment, given that we don't have a strong enough quantum computer to test them with. I won't profess to be an expert by any means on quantum resistant cryptography, but the other possibility I am aware of is an extended Merkle signature scheme, which is already in use by an altcoin. Still, by the time this becomes a serious issue in a few decades from now, then I would expect that majority of transactions will have moved to a second layer solution, hence my comment about Lightning comments.