How does Shakespeare use love to portray Romeo and Juliet as foolish in Romeo and Juliet?

I am going to take a different perspective on the play in
this response. It is easy for us analysing the play from our contemporary perspective to
underestimate the extent of the foolishness of Romeo and Juliet's actions. We live in a
culture where it is expected that we will pick our own life partner, but let us remember
that at the time of the initial performance of the play, very few people actually had
the luxury of selecting their own wife or husband. In particular, for people of Romeo
and Juliet's standing in society, marriage was something that your family organised for
you as marriage was conducted amongst the upper classes for means of wealth, prestige
and alliances. Thus, if we think about it from this perspective, it is clear that both
Romeo and Juliet were very foolish to marry in secret and to let their own feelings of
love overwhelm other, more important feelings such as their own family responsibility
and duty to their houses. Note how Lord Capulet views his own procuring of Paris as
Juliet's future husband in Act III scene 5:

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How? Will she none? Doth she not give us
thanks?

Is she not proud? Doth she not count her
blest,

Unworthy as she is, that we have
wrought

So worthy a gentleman to be he
bride?

From Capulet's
perspective, he has been a good father, finding an excellent, wealthy husband who
occupies an important position in society. Juliet therefore owes it to herself and to
her family to marry Paris. Her love for Romeo has therefore foolishly made her cherish
her own wants above those of her family.