By this definition, all monogamy would be serial, except in the very rare case where a person only loves and is in a relationship with one person for their entire life.
Yes, the argument here is that people who say "You can't love more than one person that much," can be replied to with "Most people do, just usually not at the same time."
Maybe people use the word monogamous incorrectly by adding in the idea that it implies forever, and not just exclusive while in a relationship.
As far as I know, that's what it originally meant (only one spouse in your lifetime, no sex outside of marriage). For many religious people, that's still what it means. After all, adultery technically includes sex with your spouse before you're married, too.
I think serial monogamy makes sense from a biological point of view. You find someone, stay together long enough to have a child and get them out of the most vulnerable time, then part ways and get another partner and do the same, thereby multiplying the DNA variety or something.
With that definition, the amount of time with each partner would probably be something like 3 years, which I think is the longest NRE can last, so it makes sense.
While "serial monogamy" might sound like a succession of quick relationships (but really, what's your definition of quick? 3 years can be considered quick or very long, depending) to me really the point of it is saying, "If someone new shows up, you might fall for them and stop loving the person you were previously with, and leave them."
I think it's different from lifelong monogamy, where it's assumed that if someone new comes along, it won't matter, because you have found your lifelong love.
I went to check Wikipedia's article on monogamy and found a part on serial monogamy (emphases mine):
Serial monogamy
Serial monogamy is characterized by a series of long- or short-term, exclusive sexual relationships entered into consecutively over the lifespan. [...] In common usage referring to humans, the two partners need not be married, but may be involved in a sexually monogamous relationship. This behavior is sometimes referred to as a form of,[21] or replacement for,[22] polygamy.
In animal sexuality, serial monogamy often means that an animal will have a different, but exclusive, breeding partner each mating season. Generally, any animals that do not mate with one partner, for life, but do mate exclusively with one partner per mating season can be considered serially monogamous, including those who find a second mate only upon the death of the first.
Western culture
Within Western culture, several academics have put forth the position that serial monogamy is considered more fundamental than "full" monogamy.[23][24]
Break up
Serial monogamy has always been closely linked to divorce practices. Whenever procedures for obtaining divorce have been simple and easy, serial monogamy has been found.[25] As divorce has continued to become more accessible, more individuals have availed themselves of it, and many go on to remarry.[26] It has been suggested, however, that high mortality rates in centuries past accomplished much the same result as divorce, enabling remarriage (of one spouse) and thus serial monogamy.[27][28][29]
I think as part of the polyamorous community, we tend to hear about serial monogamy in a negative light, because it can be used as an argument: "We stay with the people we love, instead of dumping them for the next one that shows up!" or equated with NRE-addiction caused serial monogamy (in which the relationships are generally much shorter and pretty much never long term at all).
EDIT: I don't think that's in itself a bad thing, the problems arise when the other party is being taken for a ride.
But outside of the polyamorous community, it seems to me that "serial monogamy" is a term that's already used, and it simply refers to the fact of having more than one partner in your lifetime, but only one at a time.
