While Reagan didn't alienate any voter, he said if individuals wanted to accept his philosophy that was fine with him, but he wasn't buying the philosophy of any group. This is what Reagan had this to say about the JBS:
"I have never been and I am not now a member of the John Birch Society, nor do I have any intention of ever becoming a member. I have never sought Birch Society support, nor do I have any intention of doing so should I become a candidate for public office. In my opinion those persons who are members of the John Birch Society have a decision to make concerning the reckless and imprudent statements of their leader, Mr.[Robert]Welch".
Ronald Reagan, September. 24, 1965, Ref: "Reagan: a life in letters", pages 171-172.
In 1980, the Public Relations Director for JBS, John McManus had said Reagan was a "lackey" for communist conspirators. Robert Welch denounced McManus for his remarks about Reagan, but later realized Reagan didn't meet his expectations as potus.
ReaganMan: The JBS, as an organization, did not (as you wrote) “oppose Reagan’s agenda for/as Governor and President”.
Some specific members of (and writers for) the JBS were hostile toward Reagan as President but, as I pointed out in my previous message, in 1980, Robert Welch announced that he planned to vote for Reagan. Mrs. Welch subsequently resigned from the JBS partly because of what she considered the unfair attacks upon Reagan in the JBS magazine.
Interestingly, many of the politicians whom the JBS scored at 100% on their “Conservative Index” (such as Sen. Jesse Helms and Cong. Ron Paul) were glowing in their praise of what Reagan accomplished -— although, in later years, Cong. Paul expressed disappointment that Reagan did not dismantle more of government.
Since the Birch Society is a highly ideological organization, and is composed of people who rarely have extensive political experience, they approach all public policy matters with absolutist certitudes. In the real-world, incremental change is the norm. Reagan was able to transform government and motivate a new generation of conservative leaders in ways which no previous Republican had ever achieved. 100 years from now, there will still be books and doctoral dissertations written about his impact upon our country -— whereas the Birch Society will be totally forgotten.