I don't think an English major is inherently more or less rigorous than another major. It's an awfully big time commitment, what with the insane amount of reading and writing. It really does hone your analytical skills in different ways from the hard sciences. It's not that one is better than another; they're different and will generally attract different people.
I'm sick of the social sciences or humanities getting a bum rap from hard-sciences devotees. I also think academics in the social sciences and humanities perpetuate the stereotype because a lot of them buy into this natural-sciences envy. They often try to shove social-science theory into a natural-sciences box. Frustrating.
Well, I wouldn't buy that reason either, but I have no real problem with the choices people make - so long as they make them for themselves.
Least for myself, and I would think more for Ps than SJs, you can generally explain it as "I know it may not be as financially viable, but I love it and can't imagine doing anything else". They may not *understand*, but they tend to accept that.
SJs? Uhh... Good luck. I haven't had any luck with them either
Edit: Another would be:
"I'm awesome, and you're not. You were asking seriously, right? I'm sorry, I tend to answer questions seriously the first time around."
They're running just like you
For you, and I, wooo
So people, people, need some good ol' love