Feminists were also branded as delusional mentally ill people when they started fighting for their rights. Your comment shows exactly why these movements need to exist and the prejudices they have to overcome. Are men fighting for basic access to their children in a biased legal system "crazies"? What about those trying to tackle the massive problem of young men committing suicide? What about those campaigning to give boys the same protection from genital mutilation as girls?
Every movement has radicals and unfortunately they tend to be the loudest. Consider the running controversy over anti-transgender feminist groups (eg. [1]). They're loud, get lots of attention but hardly represent the majority.
All MRAs I’ve ever heard were downright weird in their worldview. There are some problems worth fighting for (nothing comparable with what women faced and still face), sure, but that doesn’t seem to be their focus. Their focus seems to be demonizing feminists and derailing. (Let’s quickly talk about custody: feminists and MRAs could actually be marching in exactly the same direction: The root cause of the problem are strict gender roles, women are for taking care of children, men are for working. But no, feminists are to blame. MRAs also love using warped statistics, but that is very much besides the point. There is no reasonableness in that movement.)
The text implies that some sort of MR movement would spring up as a widespread reaction to feminism (and it doesn’t have any comparable issues to fight for, it doesn’t have the numbers, it doesn’t have the intellectual depth nor the academic backbone). It did spring up as a tiny reaction to feminism. Wikipedia tells me that the movement has its roots in the 1970s, so it’s not like this would have been something completely new in 1987. It’s hard to say, but I see no reason to believe that the MR movement is that much bigger than it was in 1987. And it still defines itself as a reaction to feminism. Which makes about zero sense. All the issues they are fighting for were not caused by feminism. Far from it. Many feminists will be perfectly capable of recognizing them as valid problems. (But, again, that’s very much besides the point.)
Feminism has a long and storied history, to which its "intellectual depth" and "academic backbone" has, and continues to be, largely irrelevant. It is not monolithic, and represents a diversity of views unified only by the idea that women should stand up for themselves. The modern custody situation, which admittedly has become more nuanced since the 1980s, is at least partly a result of strains of feminism that embraced motherhood.
While I can agree that, at present, many of the "MRA" seem like "weirdos" tilting at windmills, there is nothing inherently wrong with having strong advocates on both sides of a discussion.
If I were to guess, I'd guess that the attitude results from conflicts with other crazies. There are still a lot of feminists who demonize men and derail, for example, and the MRAs have to confront them instead of ignoring them. Those sorts of discussions result in paradigm shifts in many people.
[1] http://www.guardian.co.uk/commentisfree/2012/may/25/radical-...