I'm going to take the pro-SHA/pro-ASIC stance.

Having a single simple hashing algorithm is better than having a difficult one, or having a pool of them chosen randomly.  The reason is that it keeps the barrier to entry lowish for new ASIC producers.

You simply cannot make an algorithm that is, in general, resistant to ASICs.  If a general purpose CPU can do it, then a purpose-built CPU can do it faster.  The best you can do is make it expensive for someone to develop an effective ASIC.  Also, time is money, so if you use a random pool of algorithms, then the only people that will have ASICs are those that can afford to develop them quickly.

Building an ASIC for SHA-256 is pretty simple.  At least 3 different groups have already done it, on shoestring budgets and somewhat quickly.  Increase that to maybe dozens if you include the not-suitable-for-bitcoin streaming hasher chips that are commercially available.  If (heh) they abuse their position as first movers, the barrier to their competition is very, very low, on the order of tens of thousands of dollars and several months to get started.

Making ASIC development more difficult will keep out the people that we want to include, and do nothing whatsoever to exclude the people that some would like excluded.