The word "darn", as a verb, usually means "to mend a hole in your garment by sewing" or, as a noun, means "a hole in your garment that one has mended by sewing"; however, in this instance, "darned" is a euphemism for saying "damned". A euphemism is a polite way of saying something. For instance, I might say to someone,
"That shirt doesn't look great on you"
when I really mean,
"That shirt is damn ugly! Get it off and burn it!"
An antonym of "euphemism" is "dysphemism".
If you want to know what the "be" is in each statement above, it's the present subjunctive conjugation of "to be". The speaker, when he says,
"Love be darned"
is basically saying,
"I want love to be damned to hell"
or, if I can swear on this forum,
Every single one of those statements is damning its subject or telling it to "get lost", so to say.
I hope that might have helped you out. Take care and good luck.