They are not just "against" Trump, they are actively supporting the lib myth that the GOP is full of bigots, in order to marginalize Trump's supporters.
In that, they reveal a corruption so severe that the fact that they are against Trump IS a strong indicator that he should be the nominee.
Limiting the candidates of a brokered convention to those with major support from the party voters, is not unreasonable.
Supporting these yahoos we have in charge of the Party now, IS.
The GOP is a coalition party of wealthy oligarchs, socially conservative religious zealots, disenfranchised white voters, and right wing fringe groups, and Southern Racists who abandoned the Democrats when Johnson pushed through the Civil Rights Act. It does have the Southern racists as a significant percentage of the party.
The fact that both the GOP elite and Democrats, and people who don't even live in the US, oppose the guy should give you a clue as to how spectacularly dangerous he is considered to be by those who don't support him. The idea that a man who routinely demonstrates by his statements that he knows nothing of foreign policy or diplomacy, and who has insulted every nation he's spoken about, not to mention suggesting war crimes to deal with terrorists, who have the world's largest standing army at his disposal, not to mention the launch codes for the nukes, it's just too frightening to contemplate.
I am reminded of what someone who worked on the Trump Hotel in Toronto said to me. Trump broke ground in 2007, and the hotel, which had been announced in the early 2000's, was opened in 2011 or 2012. I could not find evidence that the building has been fully completed, as the principals have been battling in court for years. A sub-contractor friend who worked on the building said that Trump's name may have been on the building, but the Saudi's signed the cheques.
The first primary election was held in 1910. Until that time, the party bosses controlled who was the candidate for president would be. Unlike elections for political office where the Constitution and its Amendments determine who is allowed to vote, and how the process works, the political parties can set their own rules for selecting their candidates, based on whatever criteria they think is fitting and proper. They are governed by their own by-laws and rules, not the US Constitution.
It doesn't matter whether you think the selection process is fair and equitable, because there is no legal requirement that it should be.