Obviously, yes, if you keep going back to the well, eventually someone will betray you. And vesting will make a founder breakup easier (if the company can survive without the founder, and if it hasn't already been long enough that they are fully vested, and if you couldn't have come to a negotiated agreement). And that's a good reason to do it. Another good reason is if your cofounders are already pretty mercenary and the vesting incentive actually makes a breakup less likely.

There are good reasons not to do it too. If you work with good and honorable people, who have kept their promises to other people in their life, and who have (incredibly valuable) reputations as honest people to protect, they are pretty likely to keep their promises to you too. (Don't forget to actually discuss these promises!) Unless you unnecessarily move the decision to leave into the category of "rational economic decision" by putting a price on it. (And four years later, when that price has decreased to zero?)

Another reason is that you might trust your cofounders more than your possible future investors (they have reputational incentives too, but you don't know them yet!), and prefer not to give the latter a possible avenue to steal the company from some or all of you.

Sometimes there can be tax tradeoffs, depending on what else you are doing.

As I said, it might be a good choice to have vesting in many or even most circumstances. Everyone should carefully consider it. But "always no matter what" is not good advice.