Why is reacting sodium metal with dilute sulphuric acid a bad idea?

Sodium is an alkali metal; elements in this group are highly reactive with water.

Here's the general equation; alkali metal=M in this example.

2M(s) + 2H20(l) --> 2M+(aq) + 2 HO-(aq) + H2(g)

This is an incredibly exothermic reaction; the energy released from the reaction of Na and H20 is usually enough to ignite the hydrogen gas formed in the reaction.

In plain words - EXPLOSION!!

Now, I realize you are talking about dilute H2SO4, but the result is roughly similar.