Depends how far you are willing to stretch your definition of "the same".
I think the opinion that all politicians are the same is:
1. Impractical, if the underlying assumptions were true: in a democracy you got the right to vote people out who misbehave. If you are blind to the differences between those people, you are effectively letting those who are a little bit worse than the others stay. And so the spiral moves downwards and you will at some point in your life wake up and ask how it came to this.
2. Purely Self-protective: taking part in politics and being involved and observant comes at an (emotional) cost. Pretending there is no difference is an easy way of not having to get involved while still having a thinly vailed excuse to continue complaining.
3. Untrue: Each body of government will always have a few crazy corrupt politicians and some that are extremely principled (and a mixture of those things in between). Our task is to punish those who are crazy corrupt by not voting for them, where we can, while we are still allowed to vote.
4. Popularistic: Many unpolitical people share that opinion, it is not an "unpopular" opinion, it is the opinion of that drunkard you meet at the pub. If you ask them to name you politicians that are currently in positions they can't name any. If you tell tell them the name of politician A who got fined for corruption and politician B who has a Life-Long track record of doing a thing they stood for in their twenties they can't tell you the difference
5. Self-Defeating: You don't have to inform yourself, because everything is "the same" anyways. This has the downside that all it needs to get your vote is to look or feel not the same, because whether they act different is something you obviously cannot tell. It is a bit like if you ask a person who thinks "all computers are the same" to buy one for you and they select one because it had "a nice color", except that this actually has a huge impact on people's lives and maybe even the survival of the human race.