Oh yes. Attempted murder, at least, is almost viewing Snape as an equal - he has to be eliminated, he's a threat to MWPP.
The alternative is much more humiliating - it's all one big joke; Sirius not only didn't view Snape as a threat, but thought that the idea of him being scared, possibly injured was funny; and James Potter is forced to rescue helpless Snape like a little child.