Nothing wrong with pirates early game, size wise anyway. They really are free experience, but that's only so with the correct circumstances.
They do however amount to nothing later on. If I defend against them after I've got stuff set up, it's because I have a capship to level. A 200 point fleet two hours into the game might be a little much, but I'd aim for there.
That said, pirates aren't entirely free experience. If you have a spy in the star gravity well, you can track them, find out which planet they are hitting, and tag one on the opposite side shortly after to catch them away, or follow them in a little behind and catch the enemy fleet between them and you. I wiped out some of a heavily fortified planets infrastructure and caused significant damage by sending a lone sova in behind a pirate fleet once. The pirates took all the hits and I got all the credit for wiping out the enemy bombers and killing the reinforcements. The pirates themselves could have been ignored or used for xp, but with a high level sova playing havoc on your defenders you have a more pressing concern.