Take it from someone who learned the hard way, take the aspirin.
It isn't going to cause you or baby any harm, but without it you could end up very ill.
With my first pregnancy everything was fine, until labour, I had eclamptic seizures in labour (had never even heard of Eclampsia, the stage after pre-eclampsia) and spent a week in intensive care.
My son was very poorly when he was born and we both very nearly died.
I took aspirin in my second pregnant, daughter was born at 38 weeks, I developed mild pre-eclampsia.
I am pregnant with DC3 and was told to take it from the day I found out I was pregnant (blood pressure never went down from first birth)
I was young, fit and healthy, normal weight and no reason to think this would happen but it did.
It's like saying why take folic acid? because you want what's best for baby and you will do anything to reduce the risks of bad things happening.
Sorry for the horror story, but if it means what happened to me doesn't happen to you then I am happy to scare you all.