1. The EU is a great trading area. By leaving it the UK is vulnerable to other countries like US, China etc because we put ourselves in a position where we need them more than they need us. With the EU you had a big powerblock of trade that could compete with others and therefore get better trade agreements.
2. I don't even know what to say about nr 2. A lot of other countries have much better maternity/paternity leave than the UK does and the EU does not try to lower it. I'll give you a few examples. In Romania you get a choice. You can get a years paid leave (75% of your usual pay every month, unless you are on minimum wage in which case you will get minimum wage) and than if you return to work after a year you get a bonus of 500RON on top of your normal paycheck from the government. Or you can take two years leave with 75% of your usual salary. Or in Hungary it is 3 years of which for 168 days the mother is paid with 70% of her original salary which is paid by the state. After this period a mother is entitled approximately 100€ per month for the child. Bulgaria has 410 days. And these are countries that are considered "poor" and not the best places to live.
3. The reason why the UK is politically isolated in the EU is its own doing. People keep electing eurosceptic politicians into the Parliament and generally don't do a good job.
4. Those legislations are there for a reason. Just look at the old Soviet block to see how different life is without regulations. Corruption is a big problem in many of these countries and those regulations and legislations that the EU is pushing are there to make sure that any EU funding that gets there is spent correctly.

I hope this helps.

BTW I don't think that Leavers are stupid. I am an EU citizen married to a Englishman and I honestly think that a lot of British people don't see how good they have it. You did not have to fight a lot of the issues with corruption and unbalanced governments that other countries had and are still going through. Of course you had your own issues, but being part of the EU was a safety net to the people, government couldn't get away with doing whatever they wanted. You are losing that safety and I can see this place becoming 1. a tax haven for the US, 2. politically corrupt 3. even more divided between the rich and the poor.