so you get check from the bank rather than you sending a check to the bank for your mortgage. so please explain me again why that is a bad thing?
are there people who think paying 20% mortgage interest is better than paying 2% mortgage interest?
Negative interest rates are more indicative of possible underlying problems than a problem per se.
To understand this requires some background math on how/why interest rates are set. Fundamentally if I loan you $100, I will want back more than $100 because there's some risk you default. However if I think money will be worth more in the future (ie deflation, a bad thing), I can accept <$100 because that <$100 will still be more than the $100 of now. Similarly on houses/assets, if the asset will rise in value, even if you default I get the (more valuable) house and sell it for my money back. You can differentiate between these two by comparing rates, and it seems negative rates are across the board than just housing, which if these are our two options it appears more the former.
The other key option to consider is that the base rate on interest/loans is often from the central gubmint bank to private banks. The gubmint isn't bound by individual capitalist greed, and uses the rate as a control knob to regulate the larger picture. For example if more spending is necessary to keep the economy going, it can essentially create more money/spending by making borrowing it cheaper (or in this case paying people to borrow/use it). In a vacuum this creates inflation, which isn't necessarily a bad thing if other factors are causing deflation.
In the grand scheme of things none of this is caused by brexit, but uncertainty can discourage spending/investment, which the government will try to counteract. Overall the goal in modern capitalism is maintain stability and a modest inflation (and ostensibly modest interest rate).