Some Muslims argue for polygamy

because sometimes it is needed. Statistically, women almost always outnumber men in any given population. Are some women supposed to be confined to life alone because there is no man for them to marry?

But that is not true.

The Encyclopædia Britannica (15th edition) states in Volume 7, p. 998, in the section:

Genetics, Human

... Reliably, in almost all human populations studied at birth, there is a slight excess of males; about 106 boys are born for each 100 girls. Throughout life, however, there is a slightly greater mortality of males; this slowly alters the sex ratio until, beyond the age of 50 years, there is an excess of females.

This means in particular that in the usual age when people consider marriage, i.e. in the range of about 18-40 years, there are more men in each age group than women.

[See also the very detailed listing regarding sex ratios for nearly all countries of the world in the CIA Fact Book.]

The higher number of women is only AFTER the age of 50.

The following questions come to mind: Of those Muslims who practice polygamy, how many are marrying a women 50 years old or older to be their second wife or further wife? Or even their first wife?

Aren't in most polygamous marriages the additional wives YOUNG women, and as such taking away the women of suitable age from the young men who are looking for a partner?

This leads to the concluding question: Are not Muslim men who are marrying a young second wife making the already existing imbalance worse and are as such inconsiderate of the younger men since they are making it harder on them to find an appropriate wife?

The only statement about polygamy from a Muslim that I find acceptable is "Polygamy is allowed because Allah said so." Do not claim it is right or even necessary because of birth ratios etc. Because that is objectively false.

If you argue for the necessity of polygamy due to imbalance of the sexes (however this might have come about), are you willing to allow several husbands for a woman in those societies or circumstances where the balance is tilted the other way? If not, then this shows that "ratios" never was the true reason. It is only brought into the discussion to justify with some outside argument what the Qur'an states is the (permissive) will of God, but which many Muslims feel they have to defend with other arguments since they feel uncomfortable about just leaving it as "the will of God".

Further reading

A response to the claims of Zakir Naik on Polygamy
Deception as a means for support: Dr Naik's lies uncovered (off site) is a similar but less polite analysis

Women Issues
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