They should have known.

Tarek and Christina El Moussa, the hosts of HGTV’s show Flip or Flop, figured Portland would be a natural market for their traveling seminar on how to remodel and flip houses for a profit. So they scheduled four seminars in Portland to teach the tricks.

And, of course, Portland’s lefties went ballistic.

“Stay out of Portland!!,” said a typical online post. “You’re preying on low income families and marketing to out of state buyers that are pushing locals out. You are not welcome!!”

But wait a minute. If you’ve ever watched Flip or Flop, you’d know that what the Moussas do is buy generally crummy houses, invest in substantial upgrades and sell them (hopefully for a profit), substantially enhancing the neighborhood. What’s wrong with that?

Would Portland’s lefties prefer that rundown houses just sit there as eyesores in nice neighborhoods? Would they prefer that dilapidated houses sit empty, attracting vandals and squatters?

Critics of the Moussa’s visit were likely motivated, in part, by their objection to so-called gentrification, upgrades of neighborhoods driven by economic and demographic changes.

What the objectors fear is a dislodging of the local culture and its replacement by higher income, higher educated, higher status residents of all racial and ethnic populations who patronize a more upscale mix of retailers.

But gentrification, for all its negative connotations to lefties (who, by the way, are often a key part of the gentrifying population) is what turns decaying areas of cities into neighborhoods of residents and businesses who pay taxes that lead to upgrades in infrastructure and government services across the board for everybody.

If you have children who recently graduated from college or are about to, they will likely be part of this process, too, as they look for good jobs and great places to live, push up the population and housing costs in already gentrified areas and put pressure on other not-quite-there-yet neighborhoods.

As they say in Star Trek, resistance is futile.