For any campaign which accepts standard currencies (also known as fiat currency; think US dollar, Euro, GBP), credit card payments will always be available in public checkout and Virtual Terminal.
For scenarios where you want to control the payment method used, it's likely better to provide assistance to donors, either by taking donations for them via Virtual Terminal, having a person present while they are donating using public checkout, or providing instructions/recommendations in the Ask pane of that campaign.
Additionally, stay tuned! Upon the arrival of cryptocurrency and stock donations, it'll likely be possible to control which of the three you would like to accept per-campaign. As such, while it's not possible to not accept credit cards when accepting standard currency, the option to not accept standard currency at all on a campaign may become possible.
For information on all Payment Options please visit Reviewing our Payment Processor Recommendations