Actually, the phrase "alternative lifestyle" was originally devoloped as a less offensive way to say, "living in sin". Another "polite" phrase was "non-traditional family unit".
Before the "free love" sixties, anyone living in a non-traditional arrangement in America was referred to as "living in sin" or not even discussed at all. Most "non-traditional" people either lived in remote areas (such as rural polygamous groups) or very privately (such as homosexual couples). Unmarried couples were looked down upon as "shacking up". It was considered very low class and sinful to live that way.
During the sixties, almost an entire generation began to rebel against societies norms. "Free love" was the slogan. It was "in" for couples to live together without marriage, and "commune" living also became popular. No one wanted to be considered judgmental or old-fashioned (heaven forbid!) so more "acceptable" terminology was developed in the media (wishy-washy-ism).
Since that time, all kinds of household arrangements have become popular and acceptable. The traditional married mom and dad with children is becoming more rare. Homosexual couples, unmarried hetero couples, never-married moms of multiple-sired kids, etc., now demand equal status with traditional families.
"Alternative" implies something is just one other choice out of many
equally valid choices. Like "alternative" fuels. Or "satellite TV is an
alternative to cable TV." Or "the intersection was blocked, so I took the alternate route to work." It doesn't carry the "good" vs. "bad" judgment of other phrases.
Just a little "word history" lesson.