My reasons are that (a) it is still completely predictable and (b) it reduces uncertainty.
If you start out with 0% or 1% inflation and it works, then you will expect it to continue working in future years. You never need to alter the mix between fees and block reward. The future plan is to operate the currency just like it is currently operating. No uncertainty. No debates like these.
If you start out with 100% inflation and then go to 50% .... and then to 0%, you are repeatedly moving to a new and untested monetary model. At some point, you may worry that the model will cease to function. This introduces a lot of uncertainty. At the same time, for the social reasons D&T points out, even if the system fails it may be likely be impossible to fix. This makes the uncertainty issue more severe.
Despite my concerns with Satoshi's system, there is a good theoretical justification for Satoshi's model. If you want to build up a network, it is optimal to subsidize early adoption and then raise fees once people are "locked-in." Thus, you would want to have 0 txn fees and high inflation initially to subsidize adoption of bitcoin payments. Once people depend on the network, you would want to gradually raise fees.
Satoshi's probably did not expect anyone to pay attention to Bitcoin. Given this belief, the use of an extremely aggressive strategy to promote adoption would be optimal. Ex-post, the aggressive strategy becomes unfortunate.
I agree with every bit of that, but I also believe a constant absolute rate of growth (instead of % rate) has interesting merits.