The question is not how to stop this. Anyone still can put anything
to his/hers pages, and it is you who fetches the information from his
private property. Don't you never ever dare to question that.
(Ok, so some covernments do.)
The question is how a search engine can provide its customers the
most valuable information. There are many other problems here and
this one is only one of them.
This is a matter of creating better and better algorithms and
heuristics to evaluate the goodness of the match between customers
query and the information content of the page. Also the tools
to examine the query results matter. Even the plain title displayed
on the results page often says that this page is not worth looking.
Remember also that a customer is not interested to hear your
personal opinions on what is worth reading or not, or who do you not
like.
In conclusion, do not panic. Just make a note and remember it when
writing a search engine.