I don’t think anyone has any problem with the President — ANY President — taking a vacation at reasonable intervals. And yes, it’s true that even while on “vacation”, the President is still “on call”.
I believe the objections are A) THREE vacations in the first MONTH (that’s over the top), and B) Trump said he wasn’t going to do this — he was going to stay at the White House. It’s the lying and going back on his word that’s the problem.
Oh — and he seems to be spending money on travel at a MUCH faster rate than his predecessor, and Trump made it a point to complain a lot about how much money the Obamas spent whenever they went on a family vacation. We find his hypocrisy objectionable, too.