The first question is not whether users like the feature. It is whether you are allowed to put it in front of them without asking. Under the EU General Data Protection Regulation and the UK GDPR, every processing activity needs one of the enumerated lawful bases, and consent is only one of them. The European Data Protection Board's opinion on AI models confirmed that legitimate interest can serve as a valid basis for training and deploying AI models, provided the controller implements appropriate safeguards and documents a case-by-case assessment, as summarized by Wilson Sonsini.
That assessment has three parts, and the UK Information Commissioner's Office lays them out as a purpose test, a necessity test and a balancing test. The balancing test is where default-on exposure lives or dies, because it asks whether people can reasonably expect their data to be used this way. A feature that quietly summarizes a user's inbox is a harder balancing argument than one that suggests a reply the user must approve before sending. The academic treatment of the same problem notes that there is no hierarchy among lawful bases, but that consent carries validity requirements that make it impractical at scale for many AI uses, which is precisely why controllers reach for legitimate interest (Computer Law and Security Review).
In practice this means a market-by-market table, not a single global toggle. A worked example: a product team wants an AI drafting assistant default-on for all business accounts. In the EU and UK, legal runs the three-part test and documents safeguards such as output filters, a deletion path and obvious notice. In California, the analysis shifts to the state privacy statute's rules on dark patterns and opt-out rights. The rollout plan then carries a column for "lawful basis confirmed" with a named owner and a date, and nobody ships to a market where that cell is empty.



