Difficult question about "The Left".

I think it´s a mixture right now.

• Some SPD members/voters probably are still angry about Lafontaine´s "departure".
  
• In some/most West German states "The Left" consists mostly of former SPD members and union members so it seems unlikely that they themselves would be seen as extremist. Some "memory" of the old East German "SED" though probably still remains.
  
• They wanted to establish the party everywhere in Germany as fast as possible. So in some regions the party organization includes (or included) a pretty high number of former (West German) communists. These small organized groups could get a majority locally. (And these remaining West German communists are hardcore.)

Anyway the Greens needed roughly 20 years. First outsiders, then coalition partners at state level. And finally coalition partners at federal level. Always with the SPD back then.
And now coalition partner with the CDU at local and state level too.

"The Left" are a pretty "new" party. Only a few years old. And there are already red-red coalitions in Eastern Germany at the state level. The next step might be one in Western Germany.