I frequently read that it is possible to remove individual ip-addresses from SPAMHAUS blacklisting.

OK. Here is 91.205.43.252 (91.205.43.251 - 91.205.43.253) used by back3.stopspamers.com (back2.stopspamers.com, back1.stopspamers.com) in geo-cluster on dedicated servers in Switzerland.
The queries:

• http://www.spamhaus.org/query/bl?ip=91.205.43.251
• http://www.spamhaus.org/query/bl?ip=91.205.43.252
• http://www.spamhaus.org/query/bl?ip=91.205.43.253

tell that:

• 91.205.43.251 - 91.205.43.253 are all listed in the SBL80808 blacklist

And SBL80808 blacklist tells:

• "Ref: SBL80808
  91.205.40.0/22 is listed on the Spamhaus Block List (SBL)
  01-Apr-2010 05:52 GMT | SR04

  Spamming and now seems this place is involved in other fraud"

91.205.43.251-91.205.43.253 are not listed amongst criminal ip-addresses individually but there is no way to remove it individually from black listing.

How to remove this individual (91.205.43.251-91.205.43.253) addresses from SPAMHAUS blacklist?

And why the heck SPAMHAUS is blacklisting spam-stopping service?

This is only one example of a bunch.

My related posts:

• Blacklist IP database

Update:
From the answer provided I realized that my question was not even understood.

This ip-addresses 91.205.43.251 - 91.205.43.253 are not blacklisted individually, they are blacklisted through its supernet 91.205.40.0/22.
Also note that dedicated server, ISP and customer are in much different distant countries.

Update2:
http://www.spamhaus.org/sbl/sbl.lasso?query=SBL80808#removal tells:

• "To have record SBL80808 (91.205.40.0/22) removed from the SBL, the Abuse/Security representative of RIPE (or the Internet Service Provider responsible for supplying connectivity to 91.205.40.0/22) needs to contact the SBL Team"

There are dozens of "abusers" in that blacklist SBL80808.
The company using that dedicated server is not an ISP or RIPE representative to treat these issues. Even if to treat it, it is just a matter of pressing "Report spam" on internet to be again blacklisted, this is fruitless approach.
These techniques are broadly used by criminals and spammers, See also this my post on blacklisting.

This is just one specific example but there are many-many more.