I am in two minds about whether we should keep seed compost sterile or not.
Several people suggested that I use the mega compost heap compost to make up a mix to plant seeds into. Well the probability is that this mega compost heap has never heated up enough for seeds to be killed off. So using it will mean that there will be a lot of weed seed germination.
As weed seeds would probably grow faster than the vegetable seeds, competition and crowding out would mean that vegetable seed germination may be very disappointing.
We used to use a big steamer when I worked at the Glasshouse and Crops Research Institute.
We steamed the loam and mixed it with peat in the proportions that the scientists wanted. It was mixed in a big pile by hand - I know cus I was there. It is where I learnt my mixing techniques. We also threw it through a massive shredder. I had muscles the size of footballs when I eventually left that job. I suppose if I had access to a good steamer to sterilise the compost heap compost then it could be a very good seed compost or at least the main ingredient of one.
Using things like leaf mould is better because this is a little more sterile than compost heap compost. Peat is sterile and that is why it is used in commercial seed composts.
It is important for the seed to germinate within a soil community so that it can build a good immune system. Possibly this is more important to plants than it is to animals.
Now I still maintain that there is a need to keep all the pots and trays washed and clean. The build up of diseases and pests in the remains of compost at the bottom of discarded pots could be the source of such things as damping off and mildew. I would use a fairly insipid chemical like soap rather than the powerful petrochemicals that are made into fungicides.
There is a place for cleanliness especially in the greenhouse but that may not have to extend to the seed and potting compost. As Percy Thrower used to say, a tidy clean garden is a good garden and I, in the face of such gardening excellence, would never presume to disagree.