I can't speak to reform, but I can give you an anecdote about how this type of thing created trump voters.
In the 2024 election, several of my close family members planned to vote for Trump. They had legitimate concerns about both the trans issue and the large number of economic migrants, claiming to be refugees, being let into the country and consuming significant tax revenue resources. They viewed Trump as the candidate to end this. And, FWIW, he did. The border is now closed to economic migrants.
During this time, the media and left-leaning politicians continually labeled Trump voters as fascists and racists. Seeing this, I was bothered because my family members were not fascists, nazis, and racists. They are good people with legitimate concerns about immigration policy.
In addition, I simply could not believe some of the claims being made by supposedly intelligent people. "Trump is going to become a dictator!" "This is exactly like Germany in the early 1930s!" These claims demonstrated complete ignorance of the US federal and state civic structures explicitly defined in the Constitution. In order for Trump to become a dictator, he would have to gain complete control of all branches of the military. These are all completely separate branches. And they all hate each other (in a frenemy type of way). This is all intentional. Because of Trump got the Army, the Marines and Navy would respond. If he got the Air Force, Naval air assets would be deployed against the AF. There is simply no possible way for any President to gain control of all branches. That is to say nothing of individual states. Each state has its own militia (the national guard) under the control of the state's governor. Each state county has its own Sheriff and these sheriffs have immense influence. Especially in rural counties. So, somehow Trump would have to get the entire military, state militias, county sheriffs, as well as municipal police departments. And of course, there are 350+ million firearms in this country. Owned by people of all political stripes. So any type of civil military action would be met with overwhelming resistance wherein the military would suffer massive casualties. Americas have guns, and they know how to use them. This is the entire purpose of the second amendment. To give citizens the means to oppose tyrannical actions. And before anyone says "but an AR-15 can't do anything against a jet fighter!", let's remember how in Iraq, British and US troops could not overcome AK-47s and IEDs for many years. Jets don't control territory. Small arms do.
Anyway, I didn't vote for Tump in 2016. But as I saw my family members maligned by the press and politicians, I became angry. When I heard the absolute nonsense about American becoming a fascist state, I could not believe the absolute and utter ignorance of those saying it. To make it worse, these people know better. They know our systems are rock solid and organized such that this is an absolute impossibility. And yet they repeated it over and over and over again. I mean, President Obama compared Trump to Hitler and then two weeks later was sitting next to Trump at a funeral just laughing it up.
So because of my anger at the absolute worst type of false accusations as well as the stunning lies peddled about how our Federal system works, I voted for Trump. And of course, I have a young daughter. Trump's "Kamala is for they/them, Trump is for you" position completely won me over.
So I think you are right. Existing Reform voters will not be pursuaded by being called flag-shaggers. But they will become more firmly entrenched. And people who love them will be appalled by these people being falsely accused and smeared. They, like me, may decide to vote Reform simply out of spite.
You do not win elections or gain political influence by shitting on voters.