I hate the threefold repetition rule

Stalemate. The OP has made no opposition to that rule.

next he's going to be complaining about en passant

Stalemate just means no legal moves, but repetition is just repeated moves, so the point is it's still a draw.

The only rule I have beef with is the 50 move rule.

@DaveRochelson

You could stick with friendly games under FIDE rules. They excised the repetition rule for these in 2017. 

The 50 move rule and the repetition rule could conceivably be connected. The conditions for positions to be the same under the repetition rule are in art.9.2.2:

What they don't (and obviously can't) take into account is the ply count for the position under the 50 move rule. 

Suppose we have a player who is playing an endgame which his opponent can play perfectly taking into account the 50 move rule. Suppose also he is learning to play the endgame perfectly under the 50 move rule but his preparation is incomplete. Suppose further that he reaches a winning position which is drawn if the ply count is sufficiently high and he has exhaustively studied the winning line for exactly that position but with the maximal ply count for which it can still be won. Suppose even further that he has reached the position with less than the maximal winning ply count and he is not confident of winning the position with that ply count. Suppose even further than that he can arrange a repetition of the position which at the third repetition takes him up to the maximal winning ply count. He has now reached a position that he is confident of winning under the 50 move rule whereas that may not have been the case in the previous two repetitions, but even so his opponent can claim a draw under the repetition rule.

I haven't come up with a plausible example. I'll leave that to @Arisktotle.   

You don't need the 50M rule to create similar complicated win questions. Suppose the players have been moving around pieces for a year and exhausted all possible permutations once and most of them twice, then a situation might arise where it is impossible or nearly impossible to find a thin green path towards victory. With varying histories you can create an endless amount of difficult puzzles from the same diagram! There is no way any engine or tablebase is capable of handling those. Requires advanced software directed towards managing forbidden places. In general, the problem is the same as for a car driver revisiting a city where he lived 10 years ago. Now he finds that the streets are still the same but the traffic rules have changed immensely barring most of his usual routes. How to find your way 'home'?

The ply count issue has its counterpart within the repetition rule itself. Even without 50M you can still argue that the possibilities in the position after repetitions are different from the possibilities before it (and reset the rep count to 0). After all, the next move can lead to a draw (claim) after repetitions, whereas it couldn't at the first-time appearance. But we may assume that such is not the intended FIDE understanding of "repetition" and it isn't the intended understanding of repetitions + 50M rule.

The player making the same repeated checking moves should lose. Under the current rule, both players are repeating moves, but the winning player suffers and the losing player benefits. That's a bad outcome. The player doing the checks is more culpable, and should take the L. If the checking player can't force a draw but simply loses, the game doesn't go on forever; the losing player loses. 

The time to have raised an objection to this was in the 1880's.  Far too late now.

It's never too late to have a heated discussion!

With the exception of only one legal move, why would the onus be on the losing player? The other player can deviate as well, though doing so would potentially convert them into the losing player. 

It isn't always the losing player that may be willing to have the repetition and the draw. It sometimes happens that the winning player may be satisfied with a draw, and does not easily see how to convert the win or thinks that they may blunder if continuing. Or just doesnt see how to convert at all and ends up repeating trying to figure it out. The other player is under no obligation to resign, nor should they have to sit around waiting for the winning player to finally figure it out.

The rule covers all the eventualities and requires each player to be cognizant of the postion, to know when a repetition might occur so they can prevent the possibility, assuming it can be done without destroying their position/advantage.

I think you just answered your own question. What does the rule accomplish? It penalizes people who make a "stupid error". And it rewards people who can take advantage of it. That's how chess works. There are a couple other rules in chess that penalize people who make stupid errors. One is capture, another is checkmate. If you dont like any of those particular rules, there is nothing stopping you from avoiding them.

By the same token, I think I posed an interesting question. If you disagree, you're free to not respond.

I wonder if the OP believes that chess would be a finer, richer game if we got rid of the three-fold repetition rule and just kept checking forever--or until someone's flag fell

" Under the current rule, both players are repeating moves, but the winning player suffers and the losing player benefits. "

I'm afraid this is just complete nonsense. If your opponent can keep checking you forever and you can never escape, by what twisted reasoning are you winning?  

"Picture this: you're beating another player by 5, 10, 15 points."

It doesn't matter how many points your up by.  You still need to win the game.

Note that the basic chess rules are fundamentally incomplete. Though chess is a 3-results game, the rules by and large only define 2 states - winning and losing. The exceptions stalemate and impossible checkmate (deadness) constitute the minority of conditions resolving "probably drawn" chess games. The majority of draws is decided by agreement, sometimes under pressure of the clock. But what if the players don't agree and the clock does not abort? Play on forever? That's why we have the repetition rule and the 50-move rule. These are sufficient to turn chess into a decidable game, both theoretically and practically.

Even if we were to change the checking repetition - if such is definable - into a loss then we'd still have a massive amount of repetitions without one-sided checks where DaveRochelsons argument does not apply. We won't get rid of the repetition issue, we can only split it in losing and drawing repetitions. Who would applaud the extra rules?

In the Immortal game Kieseritsky was clearly winning in the final position, up a queen, 2 rooks and a bishop. It is somewhat unfair that the rules of chess allowed Anderssen to checkmate him. 

The problem with these types of posts is when the OP's uses terms like: "I was up <insert material points here> points."

I think this is a reflection on to much engine use, and a lack of understanding of the game. 

100% with you!.