Risky … if it’s automated, they could argue that you’re not actually making a conscious decision and/or not actually doing it yourself, claiming that it doesn’t apply or isn’t an unambiguous indication of your intent to knowingly opt out of whatever the next revision of the arbitration clause may be. It’s far more unclear how that would play out in (US) court than with a manual opt-out once per account per terms of service revision.
I agree that there should be more restrictions on this than there currently are in the US, but unless the composition of the US Supreme Court changes enough that they overrule their many recent arbitration-related precedents, we’re stuck with this unless and until Congress changes the law. Honestly, they’re not even legally required to allow an opt-out at all under current rulings, other than rejecting the terms of service entirely.
At least no constitutional amendment is required to fix this. These US Supreme Court rulings have been based on the Federal Arbitration Act, a regular statue, not on the Constitution (except as the source of Congress’s authority to override state law on this issue).