Ok, I'll can't just read this and not answer it.
@LifeContinues Upside of a no deal are;
Proves that government delivered their promise to leave the EU. This restores confidence in government taking into account the number of times Uk government has made manifesto promises for the purpose of being elected only to ignore once they have been elected.
Given how split the country is and will continue to be, I fail to see how adopting the most extreme interpretation of the leave vote is going to restore confidence among the 48% and even more moderate leavers. In fact the conduct of the government and Tory leadership candidates right now is the complete opposite of confidence-restoring. Even if you're right, it will evaporate fast in the face of a car-crash 'no deal' so no lasting benefit.
Potential instant savings of £39 billion. That goes a long way.
Two things: 1) that's only possible by reneging on pre-agreed commitments while a member which is going to be toxic to our international reputation, and 2) this will be wiped out by the estimated £90 billion pound hit to the Exchequer from a no-deal Brexit. It won't 'go' anywhere.
Free to trade directly with other countries without the need for EU approval. The world becomes open. Remember EU is 15% of world trade only.
As EU members we benefit from mutually agreed preferential trade deals with over 60 countries. A no deal exit ends these immediately and IIRC I think Liam Fox has secured interim arrangements with about 9 including such powerhouses as the Faroe Islands and the Palestinian Authority 
. As an independent, we are not going to get as good terms with these 60 countries as if we are part of a 28-country bloc, that's just abundantly obvious.
The EU, US, China and Japan account for almost 50% of world trade between them - the 'world' of 200+ splits all of the rest. In addition it is obviously MUCH easier to trade with your nearest neighbours geographically in terms of logistics. Doing a deal with Australia for example will be no help to your just in time industries, fresh food deliveries etc for which our economy is heavily intertwined with Europe. If there were fabulous untapped wealth lying outside those 60 deals the EU has, they'd be chasing them. 'Freedom' is a nice-sounding word that has no relation to the realities of global trade.
Europe GDP growth is nowhere near that of the developing economies which are 85% of the World economy.
Developing economies do not account for 85% of the world economy as mentioned above. In addition for trade it's volume that counts as much as growth, in addition to geography and 'fit'. Brazil may be growing fast but we don't have much call for their major exports.
UK growth as an individual country exceeds the overall growth of the EU. Reason is that it subsides the other 18 EU members who do not pay into the EU, but take money from the EU.
This is untrue. Growth in the EU and Eurozone was higher in the last 12 months than the U.K. The issues with the UK's growth cannot be explained by a net contribution to the EU which is less than 0.7% of our GDP. You're talking actual rubbish here.
No further subscriptions payable to the EU which saves UK 9 Billion per year.
Leavers are obsessed with the money we pay into the EU because it's a figure you can put a name to, unlike the benefits we obtain as a member in terms of ease of trade, access to preferential EU trade deals etc. The hit to our economy from the loss of these, not to mention the services since U.K. is primarily a services economy will easily outweigh the 'saving' on our subscriptions. What about financial services alone? The loss of passporting rights will cripple the City.
In conclusion, your 'upsides' amount to possible temporary political gain and wishful thinking.
*Downsides
This is subjective as no other EU member has left the EU before so there is no hindsight to compare with. However, here is a try:
Free trade access with EU is lost overnight until new deals are made. Chaotic transition WTO very likely*
Agreed, except substitute 'very likely' for 'certain' and maybe expand on the consequences of this such as higher food prices, crises in just in time industries, and Northern Ireland etc
Effect on GFA not clear and GFA may fall by the wayside. Hostilities that GFA was intended to eliminate may reappear
In my opinion this one downside eliminates all your putative upsides.
Not paying the exit bill may discourage other countries from trade deals
Not may, will.
Many other examples could be added for sure
Potential break-up of the U.K. as Scotland votes for independence and violence resumes in Northern Ireland
Inability to tackle the fundamental problems facing the U.K. in health and social care, deprivation, increasing inequality etc owing to ridiculous obsession with self-immolation in the cause of Brexit 'freedom'
I could go on...