In the EU, debit cards (with EU-capped interchange, and no debt mechanism) are the majority, and there's nothing that points toward that limiting low-income populations' access to banking or card networks.

Can't speak here for entire EU, only France, but opening a bank account or getting a basic debit card requires no minimum proof of income, and typically have no fees associated. No financial barrier to entry for any population segment.

There are plenty of ways for banks to make money off poor people. Some banks might defect, but the banking market is competitive, others will step in.

Make money on savings interest and mortgages?