No, you don’t see extremes on the Left anymore. Keep in mind that the extreme Left once advocated a proletarian revolution and a liquidation of the capitalist class, a dictatorship of the proletariat followed by a whithering away of the state. The extreme Left also used to advocate the abolition of private property and state ownership of the means of production.
The extreme Left also used to have Anarchists, who advocated the abolition of the state. You don’t see them anymore, although you do see their Libertarian counterparts on the Right. You don’t see or hear much about a Socialist Party in America. In fact, you don’t even see Trade Union Democrats or Social Democrats on the Left in America, although you do see them in Europe.
On the other hand, you see theocrats on the extreme Right, ranging from the evangelical Religious Right, pushing their religious agenda on the rest of us (in re: abortion, stem cell research, gay marriage, the war on drugs, and opposition to women’s rights) to the full-on theocratic Dominionist, Christian Renewal and Theocon movements who want to replace the US Constitution with Biblical Law and a council of elders who would administer the law and the government much the same way the mullahs administer Sharia Law in Muslim countries. We still have an active KKK, the Timothy McVeigh militia movement, the ultra-nationalist Minutemen patrolling the Mexican border trying to turn back the tide of illegal immigrants, and Christian white separatists in Idaho, Montana, etc. If you turn on AM talk radio, you hear almost nothing but extreme right-wing hate talk (G. Gordon Liddy and Oliver North) that makes Rush Limbaugh sound positively moderate and sane.
There isn’t any question, to anyone who actually pays attention, that the extreme Right is much more extreme than anything we have on the Left today. “Liberalism” is actually quite close to the center. Back as late as the mid 1970s, you used to have liberal Republicans (Nixon and Rockefeller). But, since Reagan, the Republican party has drifted so far to the Right, that it now considers Liberals and Liberalism “far-left.” That should tell you something.