Here's the reasoning this judge used in her ruling:
1). Twitter (the space) is considered a public forum. The tweets are Trump's free speech, not a "designated public forum". However, the replies to those tweets is a public forum meaning replies can be seen by other members of the public. The ruling also made it clear that the public has no right to speak to the President and
force him to listen/read. As mentioned earlier, Trump is free to use the Mute feature on Twitter to ignore who he wishes. He, instead, blocked people from the public forum.
2). Blocked users were free to read Trump's comments and even comment, but to do so they'd have to create a new account or other ways but the court found that this was an additional burden compared to non-blocked users. It may seem fairly insignificant, but the 1A protects against "de minimis" harms.
3). Trump, even though he created his account years before running, still operates the account in his official capacity as President and his tweets are considered offical records to be preserved under the Presidential Records Act. He's used Twitter during times he's appointed officers (like cabinet secretaries), he's removed officers, and foreign policy-related conduct. All functions of the President. In essense, while the account is listed as his personal account, he's used it as a presidential account and used it to "take actions that can only be taken by the President as President".
Also, and maybe more importantly, Trump had White House Social Media Director and Assistant to the President Daniel Scavino cloesly involved in his "personal" Twitter account.
I think each of those reasonings have some level of plausibility. However, previous rulings (
Van Orden v. Perry) have pointed to the President being able to speak from his position and his words not necessarily being those of the govt.
Most people recognize that Trump going out and making his "ra-ra" speaches are him as a person and not necessarily the President and the case about falls under the Establishment Clause of the 1A that essentially means that while the govt. is prohibited from endorsing a religion, governmental officials can express their religious views as individuals. Using that same case and Establishment Clause scenarios, I think it'll be hard for Trump to argue he can use governmental officials/staff to manage his personal Twitter account that is supposedly expressing his personal opinion/speech.
On the flip side, it's clear Trump's personal account is personal. He advocated for peopel to vote for certain politicians, complained about fake news, witch hunts, John Kerry, correspondents' dinner, and a number of other things that are obviously connected to him personally. This case was brought on by a group that only complained about being blocked by Trump's persdonal page, but not offical pages such as @POTUS, @PressSec, or @WhiteHouse, but this judge ruled that because he used WH staff, that it's no longer personal.
Now, to a point brought up by you and others, your right to free speech doesn't force anyone to listen to you. In 1984, SCOTUS ruled (in
Minnesota BD. for Community Colleges v. Knight) that a "person's right to speak is not infringed when government simply ignores that person while listening to others." Your example of a heckler is perfect here.
Just as Trump has the ability to use the Mute function, the DoJ appeal will likely point to the fact that people can log out of twitter to see Trump's tweets or use incognito mode. This would be an argument for a "de minimis" harm.
It'll be appealed, but the decision will affect both sides of the aisle because both Democratic and Republican politicians across the country have blocked people. The judge in this case did not issue and injunction (that would force Trump to unblocked those people), only saying:
This only means that, should Trump choose to appeal (seems likely) Trump can't/doesn't have to ask for a stay pending the appeal.
