Perhaps I worded that somewhat confusingly. I'm in favor of privacy regulations existing in the first place. What I'm against is having privacy regulations suddenly become stricter below age 18. Most website operators want to minimize the time and money spent on compliance, and the lowest-friction way to do that is to implement a privacy-invasive age gate and deny any user who does not pass it. (Either the website receives your identity directly, or the government learns which websites you've been accessing. I've since been informed that less invasive age gates are technically possible, but they would require competent regulations to implement.)
The usual ethical difference, as I've understood it from prior discussions, is that a legal adult user can always consent to a company using their data, so long as the data is knowingly given to the company, the user has been honestly informed of what that data is used for, and the user can revoke the company's access to their data at any point. (Some people recognize less-strict conditions as acceptable, I'm just taking these as a baseline.)
However, many of these new regulations outright prohibit minor users' data from being used in certain ways, even if those users have freely consented to it, with the justification that minors are unable to evaluate the full consequences of their data being used. Since businesses face major liability for violating these regulations, they have two options: either implement the strictest possible age-related regulation for every user, or implement an age gate that cannot be circumvented short of the user committing fraud.
In this particular regulation, some of the wording is vague, requiring a "compelling reason" to collect minor users' data, regardless of those users' consent. Businesses abhor that kind of liability: how do they protect every user as if they might be a vulnerable minor, under every possible interpretation of the regulation? The easier path by far is to require an age gate.
Thus, I'd argue that the better path would be to require uniform privacy regulations, recognizing that random websites don't want to be in the business of age verification. Either require the same strong privacy regulations for all users, or don't implement the new regulations for minors at all.