Someone please tell me what is so WRONG with putting a wall on our BORDER

Someone please tell me what is so WRONG with putting a wall on our BORDER, to stop anyone and everyone from coming into the country illegally. And the democrats will shut down government to not let it go up??
<< Friday is the deadline for Congress to pass a budget to prevent a government shutdown, but Democrats insist that they will vigorously oppose any money for a border wall in a new spending bill. Getting the funding for the border wall will fulfill a major promise President Trump made on the campaign trail, part of which was to bolster national security and stem the tide of illegal immigration. From the The Washington Post: “The Democrats don’t want money from budget going to border wall despite the fact that it will stop drugs and very bad MS 13 gang members,” Trump tweeted Sunday morning. In a subsequent tweet, he wrote: “Eventually, but at a later date so we can get started early, Mexico will be paying, in some form, for the badly needed border wall.” >>