Possibly Trotsky whose modification to Marxism (skipping the bourgois phase) gave credence to what turned into materially sub optimal mess.
Hezzbollah and Hamas have not done themselves any favours, I’m not sure that they qualify as they are people plural rather than individuals.
People, please try to remember that this is a list, not a debate.
Thank you.
On the other side Betty Friedan made an issue out of lesbians in the feminist movement that didn’t endear her to the movement and made people outside the movement see lesbians as a threat.
Dworkin, MacKinnon, et.al. - with the “sex=rape” meme set feminism back as well, with so many women who are philospophically feminists unwilling to identify themselves as such because of the extremists.
Martin Luther. He really just wanted to change the Catholic church. Instead he ended up creating a whole new sect of Christianity and still had the same old Catholic church.
Mikhail Gorbachev only wanted to reform the Soviet Union, but set in motion a series of events which eventually destroyed it.
Who made the decision to sink the Lusitania? That’s gotta be #1.
Also, I’m no expert, but if Zacco and Vanzetti were guilty, they’d be top ten.
Could I also mention my mother, who really wanted me to be a lawyer? 
But as has already been pointed out, Jesus Christ didn’t found Christianity. He was a Jew through and through. You would have a much stronger argument against St. Paul.
In any event, the problem with your position is that it can be easily argued that a world without Christianity would simply have had the same number of people slaughtered in the name of some other religion. In order to find good nominations for this list, we don’t just need people who espoused one thing but something else happened. We need people without whom the something else wouldn’t have happened.
Take good old Adolf Hitler. It’s quite reasonable to construct a scenario in which, without Hitler, World War II DOESN’T happen; without his force of personality it’s likely the confrontation wouldn’t have escalated to military levels and if it had would not have exploded as badly as it did. But WITH Hitler, Germany was razed to the ground, millions of its people killed, and its territory reduced - the precise opposite of what he wanted.
However, I think the grand champion of all time must surely be Francisco Solano Lopez, the president of Paraguay who launched the War of the Triple Alliance, which effectively destroyed the country and killed more than half the country’s population.
Assuming that their cause is anything other than: Get themselves in the newspaper, Jesse Jackson and Al Sharpton come to mind.
Not fair. The Council of Trent truly addressed many of Luther’s complaints largely as a response to the reformation that Luther began. In particular, it attempted (fairly successfully, IIRC) problems with priests such as lack of education and lack of moral or spiritual solidity. It further lowered the role of politics in the appointment and functioning of church officials. Luther’s actions definitely were not counterproductive.
I’m normally against the idea that people should be eaten by bears, but in this case I’ll make an exception…!
Not really in the same league as dictators and political leaders, but still worth mentioning:
Doing A Ratner
I think a lot of Environmentalists (at least the ones like Greenpeace who seem to get all the airtime) do a lot of harm to their own cause.
Refusing to accept that nuclear power is a viable alternative to coal and oil power is a good example of this and the spokesmen that the media seem to dig up for environmental issues tend to put a lot of people off (as an example, BBC Newsnight ran a series last year entitled “Ethical Man” - as part of this, the presenter visited some guy who manages to live with just a gallon of water a day (or something like that). Unfortunately, whilst it’s important not to waste water, this guy’s house looked like a shanty, his clothes were grubby and he looked completely unkempt. The impression it gave was that caring about the environment implies having to live like a troglodyte - not exactly appealing!)
How about Antonio López de Santa Anna? Attempting to make an example of a rebellious province and centralize authority in Mexico City, he leads a disastrous military expedition that results in an independent Texas and his own imprisonment. Nine years later he leads Mexico during the Mexican-American war, which results in Mexico losing almost half its territory. He had to flee the nation at least four times during his life (although, to be fair, he did seem to be pretty successful at getting invited back) and died penniless and ignored by the Mexican government.
Michael Moore, anyone?
PETA.
{{{SHAKES}}}
Can’t stand them…
Senator Joe McCarthy single-handedly destroyed his own cause. By being such a raving paranoid witch-hunter, he tainted all of his fellow anti-communists and security-minded folks with the image of lunacy. The KGB considered him an unwitting ally. After his spectacle, they could proceed with their subversive activities knowing that anyone who investigated too deeply could be accused of going on a witch hunt.
James Watt, Reagan’s secretary of the interior, was under fire for being prejudiced. To show that he wasn’t, he held a press conference where he announced that he had “a black, a woman, two jews, and a cripple” in his office. This went over so well that he resigned from office shortly thereafter.
Norma McCorvey (aka Jane Roe) is now a staunch pro-lifer. Of course, it wasn’t her cause at the time.
Al Sharpton and his role in the Tawana Brawley case. I hate to say it, too, since for the past 10 years or so I’ve thought he’s really spoken well, sensibly, and eloquently about the cause. But the Brawley thing just turned me off; she was clearly an adolescent truant and the situation ended up messing up up the lives of some wrongly accused people.
What exactly did he do to harm the grizzly bears (besides give one or two the taste for human flesh)? There was no grizzly backlash from his death, nor did his outreach and efforts toward conservation backfire somehow because of his actions.