I disagree. If you are healthy and in reasonable condition yet can't swim 25m without gasping for air, then you are doing something fundamentally wrong with your technique, and no amount of swimming slower will make you faster.
I see a number of people (swimmers and triathletes) who are not going to get faster until they either improve their technique or start swimming harder. They all swim plenty of yards.
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"Go yell at an M&M"