Do all participants have to create an account with a password-protected log-in?

Most of the authors for our conference will also register as participants. Thus the password-protected login for their accounts makes sense since most of the data has already been stored and can now be used for participant registration.
But is there an option for users who are only participants to register without having to create a password-protected user account?

No, an option for registering as a participant without creating a user account as the first step is not available.
There are several reasons for (and advantages of) this approach:

• Organizers get the personal details and the e-mail address of the (prospective) participant during the first step of the registration process. Suppose prospective participants do not complete the other steps of the participant registration for some reason. In that case, you can contact them later by e-mail and send them a reminder to finish their participant registration. They can then use their user account without having to enter their personal details again.
• The personal data of the user account (e.g., name, address, country) is required for the registration anyway. Otherwise, the organizers cannot create invoices, etc. In most countries, organizers and participants need valid invoices for legal reasons.
• In accordance with GDPR, users have to confirm that their personal data may be stored online. It makes sense to ask for this confirmation during the first step of the registration when they also enter their personal data, before any data is saved or processed.
• The user account allows participants to log into their accounts after they have finished the registration process. They will get access to e.g., invoices, payment details and confirmation of participation. The password-protected login secures their personal information from being accessed by third parties.
• If you are using an online payment system like PayPal, Stripe, etc. payments from international participants may fail for security or other reasons. Often participants have to contact their bank first and to ask them to allow this international payment first. Without login, they would not be able to return to the payment page later.
• If you are concerned that entering a username and password will hold some people back from proceeding: There is also an option that allows your participants to generate username and password automatically.