How valid is the ISIS=Hamas equivalence?

A lot of people have been comparing Hamas to ISIS lately, and Hussein Ibish lashed out at them yesterday:

This Hamas=ISIS Israeli hasbara campaign is beyond pathetic. Really miserable stuff, and no need for it. Hyperbole is transparently idiotic.
— Hussein Ibish (@Ibishblog) August 21, 2014

In response to a question from Clifford May, president of the Foundation for Defense of Democracies , Ibish said that the answer was "too basic:"

@CliffordDMay I cannot give you Middle East and IR 101 on Twitter. Too basic. If you want to hold a panel on this and discuss with me, ok.
— Hussein Ibish (@Ibishblog) August 22, 2014

The thread went on:

Ibish didn't really argue anything in this thread, he's just making assertions.

There are some differences between Islamist groups. Hamas has fought against Salafi groups in Gaza, for example. Al Qaeda once criticized Hamas - believe it or not, for targeting civilians!

But while the tactics of the groups differ their goals do not. Perhaps to Ibish these are fundamental differences, but I believe that the differences are tactical, not strategic.

The overriding goal of an Islamic caliphate is the most important issue. Of course they disagree with each other; when have Arabs ever been unified? But given the same goals and roughly the same disregard for human rights, the differences are much less than their commonality.

Because all three groups will do whatever they deem necessary to reach their goals.