Taking out the 2nd baseman

[rwest]

In baseball and I believe in Softball as well it is legal to slide into second with the object of taking the 2nd baseman off of his feet in order to break up the double play. Based on Rule 8-7-P, why do we allow this?

The rule says that...

When, after being declared out or after scoring, a runner intentionally interferes with a defensive player's opportunity to make a play on another runner. The runner closest to home plate at the time of the interference shall be declared out.

Also, how do you interpret "opportunity to make a play on another runner"? If the defense had no way of getting the out, even without the interference, do we enforce the interference? Do we call someone out?

For example, if the BR was well passed 1B when the runner interferred with the 2nd basemans attempt to turn the double play, should we call the runner closest to home out?

If there was no opportunity to make a play, then what do we do? Nothing? If we wait to see if there was a legitimate chance to get an out, then the interference call will be delayed in some cases. If we call "Dead Ball" on the interefence and then determine there was no chance of getting the out, what do we do then?